UCDN is not updated yet.

Fixes https://github.com/behdad/harfbuzz/issues/251

Fixes https://bugs.freedesktop.org/show_bug.cgi?id=82306

Though, looks like gcc was smart enough to produce the same code
before...

Old table was from 6.2.  Remove hard-coded Mongolian and Phags-pa data.
This completes support for new scripts Manichian and Psaltar Pahlavi.

In anticipation of Unicode 7.0 data coming in the next commit.

No functional change.

No functional change.

No functional change.

No functional change.

Nothing changed...

Such it wouldn't apply to pointers accidentally.

Not hooked up yet.

Where causing issues for people with MSVC.

So we can liberally use the simple features of C++ that parts of the
codebase is already using.

Mandaic was added to Unicode 6.0, but the joining data was not updated.
Draft ArabicShaping.txt from 6.1 includes the joining data for Mandaic.
Use that.

Add variant integers to buffer item types.  More cleanup coming.

Previously boolean features turned on the entire feature mask.  This is
wrong if feature is Alternate and user has provided values bigger than one.
Though, I don't think other engines support such corner cases.

It's tested now.  It works!

Not tested yet.