Minor
[OTLayout] Correctly skip Default_Ignorable when match_func not set

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%)
Move code around
Fixup previous commit

Was not decreasing num_items.  Ouch!
Port TrueType-kerning to use skippy iterator

It skips joiners and default ignorables now.  Skips marks too, but only
if there is proper GDEF classes for marks.
Minor
Always create sub-blobs in MEMORY_MODE_READONLY

This fixes a design bug with sanitize and sub-blobs that can
cause crashes.  Jonathan and I found and debugged this issue
when we tested a corrupt font with the md5sum / filename:
ea395483d37af0cb933f40689ff7b60a.  Two hours of intense
debugging we found out that the font has overlapping GSUB/GPOS
tables, and as such, sanitizing the second table can modify
the first one, which can cause all kinds of undefined behavior.

The correct way to fix this is to make sure sub-blobs are
always created readonly, since we consider the parent blob
to be a shared resource and can't modify it, even if it *is*
writable.

This essentially makes the READONLY_MAY_MAKE_WRITABLE mode
unused...  Maybe we should simply remove / deprecate it.
Fix blob test to match c3ba49b6fa1865e8318926eaa6c0f2063d1053bb
0.9.13
Add HB_DEBUG_VERBOSE

Only affects the verbosity of function name printing right now.
Give up sanitizing after 100 edit requests

Such fonts are *definitely* really broken.  Give up.
Limits time spent in sanitize for extremely / deliberately broken
fonts.  For example, two fonts with these md5sum / names:

  9343f0a1b8c84b8123e7d201cae62ffd.ttf
  eb8c978547f09d368fc204194fb34688.ttf

were spending over a second in sanitize!  Not anymore.
Fix "comparison between signed and unsigned" warnings

Patch from Jonathan Kew.
Merge branch 'master' of git://anongit.freedesktop.org/harfbuzz