This is a bunch of hacks for now.

Improves Bengali a bit.

Gurmukhi failures half now.  Others changed slightly.

Malayalam failures go way down.  Other scripts benefitted slightly too.
Sinhala had one or two test regressions, but...

Fixes 20 out of 48 failing Oriya tests.  Failure rate down to 0.066% now.

Oriya failures down from 0.65% to 0.20%.

Fixes most Malayalam failures.  Down from 1.6% to 0.38% now.  Fixes a
few more in other scripts too.

If x is not constant, we cannot ASSERT_STATIC on it.

Apparently this was approved in Feb 2012.  No font yet.

Althought IndicMatraCategory.txt classifies it as Top_And_Right matra,
it does not have Unicode decomposition, and Uniscribe does not do
anything special about it either.

Gujarati failures down from 0.672% to 0.0130966%.

Now that we break syllables on Halant,ZWNJ, this code can be simplified.

That's really what Uniscribe does, and explains a lot of pecularities of
Halant,ZWNJ before the base.

Sent Telugu from 1% failures to 0.03%.  Improved Kannada and Malayalam
slightly.  Fixed half of Bengali, and did NOT break anything!

Specifically, don't apply 'init' if previous char is a joiner.

Fixes some more of Bengali.

Fixes more of Telugu, Kannada, and Oriya.

May break things (outside Indic...), but we cannot think of any font relying
on this immediately.

Not tuned, just copied from step 2.  Fixes another 0.5% of Kannada
failures.  1% to go.

Fixes a few Devanagari, half of remaining Kannada failures, quarter for
Telugu, and others slightly improved or unchanged.

Fixes 5 Devanagari failures, and no regressions.

Brings down failures with Lohit-Telugu from 57% to 1.40%.

Kannada failures down from 3.5% to 2.93%.

It's not in IndicSyllabicCategory.txt.  Fixes most of Gurmukhi failures.
Failures down from 7.7% to 0.222%!

For Khmer, all consonants are subjoining.  No need to look in the font.
We were looking in the wrong order anyway.

Fixes 1.5% more failures for Telugu, 2% for Kannada.
Breaks one test in Devanagari.

Fixes another 5% of Kannada failures.

Fixes most failures of Oriya, and improves others a bit.

Untested.

Following what the spec says.

Brings down Telugu failures from 40% to 3.75%, and Kannada failures from
44% to 10%.  Does NOT affect other scripts' test results.