Without the element-type they will be getting garbage, at least with
Python.

Fixes coretext notdef loop consisting of all default_ignorable glyphs

https://code.google.com/p/chromium/issues/detail?id=464755

I misunderstood how which works.

Of course, we don't really run it, autoreconf does.  We just
err if neither is available.  glibtoolize is the name it is
shipped under on OS X.  Reported by Adam.

In hb-coretext, when we were using scratch buffer for book-keeping,
a reverse_range() caused by the notdef-insertion loop could mess up
our log_clusters.  Ouch!

Fixes https://github.com/behdad/harfbuzz/pull/88

Before, the IntType::cmp functions providing this and was truncating
the hb_codepoint_t to 16bits before comparison.  I have no idea how
this was never discovered, and I'm too lazy to try to reproduce this
with Pango (which uses non-16bit codepoint numbers for missing glyphs).

I was hoping to see a nice speedup, but it resulted in a very minor one.

Shouldn't be needed.  I have a hard time imagining this breaking any
legitimate use case.

Needed some rework of Extension table.  Hopefully I got it right, and
the new template usage doesn't break any compilers...

No functional change right now.

This makes a lot of code safer.  We only try modifying the object in one
place, after making sure it's safe to do so.  So, do a const_cast<> in
that one place...

Can be further optimized, but I think I didn't break anything.

Saves another 3% off Roboto shaping.