No flag is safe, over time... See previous commit.

This reverts commit 5a330575.

Proper fix coming soon.

Fixes https://github.com/behdad/harfbuzz/issues/503

Part of https://github.com/behdad/harfbuzz/issues/509

* Undone change for Tibetan vowel u

* removed comment on reordering that became invalid with roll-back

* Support for Dzongkha contractions with multiple vowel-signs

* Removed non-functional and unnecessary defines for HB_MODIFIED_COMBINING_CLASS_CCC138,140

Fixes https://github.com/behdad/harfbuzz/issues/237

Note that Uniscribe enforces a certain syllable order.  We don't.
But with this change, I get all of the tibetan contractions pass
with Microsoft Himalaya font.

Fixes https://github.com/behdad/harfbuzz/issues/169

Addresses
https://github.com/behdad/harfbuzz/commit/6e6f82b6f3dde0fc6c3c7d991d9ec6cfff57823d#commitcomment-14248516

The feature is enabled for any character in the Arabic shaper.
We should experiment with using it for Arabic subtending marks.
Though, that has a directionality problem as well, since those
are used with digits...

Fixes https://github.com/behdad/harfbuzz/issues/141

See discussion here:
https://github.com/behdad/harfbuzz/commit/81ef4f407d9c7bd98cf62cef951dc538b13442eb

There's no way to disable this fallback, but I don't think it would
be needed.  Let's hope for the best!

Fixes https://github.com/behdad/harfbuzz/issues/153

This resurrects the space fallback feature, after I disabled
the compatibility decomposition.  Now I can release HarfBuzz
again without breaking Pango!

It also remembers which space character it was, such that later
on we can approximate the width of this particular space
character.  That part is not implemented yet.

We normalize all GC=Zs chars except for U+1680 OGHA SPACE MARK,
which is better left alone.

And add check to FLAG()

This reverts bf029281 and fixes it properly.  That commit
was not enough as it was only inheriting the shaping_action
for prev_action, but not curr_action.

Micro-test added.

https://code.google.com/p/chromium/issues/detail?id=393896

Simplifies hb_in_range() calls as the type can be inferred.
The rest is obsessiveness, I admit.

Based on suggestion from Andrew Glass.

Test: U+0F40,0FC6,0F83

[unicode] Exclude the Jamo Filler characters from Default_Ignorable, as some fonts want these to be visible/spacing glyphs.

See discussion on mailing list.

Implemented as a hack for now.  Myanmar failures down from 23 to 15.

MYANMAR: 1123868 out of 1123883 tests passed. 15 failed (0.00133466%)

The remaining 15 cases are all where the syllable is wrong according to
the OpenType spec.  We insert dottedcircle.  Uniscribe fails to do that,
but it also fails to reorder the prebase-reordering medial-Ra.  So it
gets it wrong.

That's really the logic desired.  Except that MONGOLIAN VOWEL SEPARATOR
is not default_ignorable but it really should be.  Reported to Unicode.

Based on suggestion from Konstantin Ritt.

It's considerably faster than the fallback implementation we had
previously!

Implemented for Arabic, Hebrew, and generic marks.
Activated if no GPOS table present.

Lifted from https://bugzilla.mozilla.org/show_bug.cgi?id=728866