Normally if you want to, say, conditionally prevent a 'pref', you
would use blocking contextual matching.  Some designers instead
form the 'pref' form, then undo it in context.  To detect that
we now also remember glyphs that went through MultipleSubst.

In the only place that this is used, Uniscribe seems to only care
about the "last" transformation between Ligature and Multiple
substitions.  Ie. if you ligate, expand, and ligate again, it
moves the pref, but if you ligate and expand it doesn't.  That's
why we clear the MULTIPLIED bit when setting LIGATED.

Micro-test added.  Test: U+0D2F,0D4D,0D30 with font from:

[1]
https://code.google.com/a/google.com/p/noto-alpha/issues/detail?id=186#c29

Patch from Jonathan Kew.

This reverts commit d5bd0590.

The reasoning behind that logic was flawed and made under
a misunderstanding of the original problem, and caused
regressions as reported by Jonathan Kew in thread titled
"tibetan marks" in Oct 2013.  Apparently I have had fixed
the original problem with this commit:

  7e08f125

So, revert the faulty commit and everything seems to be in good
shape.

See:
http://lists.freedesktop.org/archives/harfbuzz/2013-April/003101.html

Impact should be minimal and positive.

Currently unused.

Currently unused.

No functional change.

Shouldn't change behavior at all, but is faster / more robust.

Commit 6b65a76b.  "end" was becoming
negative.  Was trigerred by Lohit-Kannada 2.5.3 and the sequence:
U+0CB0,U+200D,U+0CBE,U+0CB7,U+0CCD,U+0C9F,U+0CCD,U+0CB0,U+0C97,U+0CB3
Two glyphs were being duplicated.

Previously we only supported recursive sublookups with
ascending indices.  We were also not correctly handling
non-1-to-1 recursed lookups.

Fix all that!

Fixes the three tests in test/shaping/tests/context-matching.tests,
which were derived from NotoSansBengali and NotoSansDevanagari
among others.

During GSUB, if a ligation happens, subsequence context input matching
matches the new indexing.  During GPOS however, the indices never
change.  So just go one by one.

Fixes 'dist' positioning with mmrtext.ttf and the following sequence:

  U+1014,U+1039,U+1011,U+1014,U+1039,U+1011,U+1014,U+1039,U+1011

Reported by Jonathan Kew.

See email thread "Skipping Control for Attaching Marks using OpenType"
from earlier this month.

If there's a mark ligating forward with non-mark, they were
inheriting the GC of the mark and later get advance-zeroed.
Don't do that if there's any non-mark glyph in the ligature.

Sample test: U+1780,U+17D2,U+179F with Kh-Metal-Chrieng.ttf

Also:
Bug 58922 - Issue with mark advance zeroing in generic shaper

After the Ngapi hackfest work, we were assuming that fonts
won't use presentation features to choose specific forms
(eg. conjuncts).  As such, we were using auto-joiner behavior
for such features.  It proved to be troublesome as many fonts
used presentation forms ('pres') for example to form conjuncts,
which need to be disabled when a ZWJ is inserted.

Two examples:

	U+0D2F,U+200D,U+0D4D,U+0D2F with kartika.ttf
	U+0995,U+09CD,U+200D,U+09B7 with vrinda.ttf

What we do now is to never do magic to ZWJ during GSUB's main input
match for Indic-style shapers.  Note that backtrack/lookahead are still
matched liberally, as is GPOS.  This seems to be an acceptable
compromise.

As to the bug that initially started this work, that one needs to
be fixed differently:

  Bug 58714 - Kannada u+0cb0 u+200d u+0ccd u+0c95 u+0cbe does not
  provide same results as Windows8
  https://bugs.freedesktop.org/show_bug.cgi?id=58714

New numbers:

BENGALI: 353689 out of 354188 tests passed. 499 failed (0.140886%)
DEVANAGARI: 707305 out of 707394 tests passed. 89 failed (0.0125814%)
GUJARATI: 366349 out of 366457 tests passed. 108 failed (0.0294714%)
GURMUKHI: 60706 out of 60747 tests passed. 41 failed (0.067493%)
KANNADA: 951030 out of 951913 tests passed. 883 failed (0.0927606%)
KHMER: 299070 out of 299124 tests passed. 54 failed (0.0180527%)
LAO: 53611 out of 53644 tests passed. 33 failed (0.0615167%)
MALAYALAM: 1048102 out of 1048334 tests passed. 232 failed (0.0221304%)
ORIYA: 42320 out of 42329 tests passed. 9 failed (0.021262%)
SINHALA: 271666 out of 271847 tests passed. 181 failed (0.0665816%)
TAMIL: 1091753 out of 1091754 tests passed. 1 failed (9.15957e-05%)
TELUGU: 970555 out of 970573 tests passed. 18 failed (0.00185457%)
TIBETAN: 208469 out of 208469 tests passed. 0 failed (0%)

Was not decreasing num_items.  Ouch!

When a match_func was not set on the matcher_t object (ie. from GPOS),
then the Default_Ignorables (including joiners) were never skipped.
This meant that they were not skipped as they should during GPOS
matching.  Fix that.

A few Indic numbers have "regressed": BENGALI and DEVANAGARI went
up from 290 and 58 respectively, but in both cases new results are
superior to Uniscribe, as they apply GPOS when we weren't (and
Uniscribe isn't) before.
BENGALI: 353686 out of 354188 tests passed. 502 failed (0.141733%)
DEVANAGARI: 707305 out of 707394 tests passed. 89 failed (0.0125814%)
GUJARATI: 366262 out of 366457 tests passed. 195 failed (0.0532122%)
GURMUKHI: 60706 out of 60747 tests passed. 41 failed (0.067493%)
KANNADA: 950680 out of 951913 tests passed. 1233 failed (0.129529%)
KHMER: 299074 out of 299124 tests passed. 50 failed (0.0167155%)
LAO: 53611 out of 53644 tests passed. 33 failed (0.0615167%)
MALAYALAM: 1047983 out of 1048334 tests passed. 351 failed (0.0334817%)
ORIYA: 42320 out of 42329 tests passed. 9 failed (0.021262%)
SINHALA: 271539 out of 271847 tests passed. 308 failed (0.113299%)
TAMIL: 1091753 out of 1091754 tests passed. 1 failed (9.15957e-05%)
TELUGU: 970555 out of 970573 tests passed. 18 failed (0.00185457%)
TIBETAN: 208469 out of 208469 tests passed. 0 failed (0%)

Originally we meant to match backtrack/lookahead across syllable
boundaries.  But a bug in the code meant that this was NOT done for
backtrack.  We "fixed" that in 2c7d0b6b,
but that broke Myanmar shaping.

We now believe that for Indic-like shapers (which is where syllables are
used), all basic shaping forms should be fully contained within their
syllables, so now we limit backtrack/lookahead matching to the syllable
too.  Unbreaks Myanmar.

Not for Arabic, but for Indic-like scripts.  ZWJ/ZWNJ have special
meanings in those scripts, so let font lookups take full control.

This undoes the regression caused by automatic-joiners handling
introduced two commits ago.

We only disable automatic joiner handling for the "basic shaping
features" of Indic, Myanmar, and SEAsian shapers.  The "presentation
forms" and other features are still applied with automatic-joiner
handling.

This change also changes the test suite failure statistics, such that
a few scripts show more "failures".  The most affected is Kannada.
However, upon inspection, we believe that in most, if not all, of the
new failures, we are producing results superior to Uniscribe.  Hard to
count those!

Here's an example of what is fixed by the recent joiner-handling
changes:

  https://bugs.freedesktop.org/show_bug.cgi?id=58714

New numbers, for future reference:

BENGALI: 353892 out of 354188 tests passed. 296 failed (0.0835714%)
DEVANAGARI: 707336 out of 707394 tests passed. 58 failed (0.00819911%)
GUJARATI: 366262 out of 366457 tests passed. 195 failed (0.0532122%)
GURMUKHI: 60706 out of 60747 tests passed. 41 failed (0.067493%)
KANNADA: 950680 out of 951913 tests passed. 1233 failed (0.129529%)
KHMER: 299074 out of 299124 tests passed. 50 failed (0.0167155%)
LAO: 53611 out of 53644 tests passed. 33 failed (0.0615167%)
MALAYALAM: 1047983 out of 1048334 tests passed. 351 failed (0.0334817%)
ORIYA: 42320 out of 42329 tests passed. 9 failed (0.021262%)
SINHALA: 271539 out of 271847 tests passed. 308 failed (0.113299%)
TAMIL: 1091753 out of 1091754 tests passed. 1 failed (9.15957e-05%)
TELUGU: 970555 out of 970573 tests passed. 18 failed (0.00185457%)
TIBETAN: 208469 out of 208469 tests passed. 0 failed (0%)

Not used yet.  Next commit...

When matching lookups, be smart about default-ignorable characters.
In particular:

Do nothing specific about ZWNJ, but for the other default-ignorables:

If the lookup in question uses the ignorable character in a sequence,
then match it as we used to do.  However, if the sequence match will
fail because the default-ignorable blocked it, try skipping the
ignorable character and continue.

The most immediate thing it means is that if Lam-Alef forms a ligature,
then Lam-ZWJ-Alef will do to.  Finally!

One exception: when matching for GPOS, or for backtrack/lookahead of
GSUB, we ignore ZWNJ too.  That's the right thing to do.

It certainly is possible to build fonts that this feature will result
in undesirable glyphs, but it's hard to think of a real-world case
that that would happen.

This *does* break Indic shaping right now, since Indic Unicode has
specific rules for what ZWJ/ZWNJ mean, and skipping ZWJ is breaking
those rules.  That will be fixed in upcoming commits.

Should NOT change behavior, since first glyph is a match.