These are frozen, so good time to add.

To make a release...

Apparently some clients have reference-table callbacks that copy the table.
As such, avoid loading 'glyf' table which is only needed if fallback positioning
happens.

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.

From http://www.babelstone.co.uk/Tibetan/Contractions.html

Update opentype language tags

Fixes https://github.com/behdad/harfbuzz/issues/234

To make room to remember Mongolian Free Variation Selectors.
Part of fixing https://github.com/behdad/harfbuzz/issues/234

Unbreak build on Windows CE

0475ef2f broke the build by using
vsnprintf(), which is not defined on Windows CE

Improve DirectWrite backend

Ouch.  Had broken it in 9a13ed45

Fixes https://github.com/behdad/harfbuzz/issues/238
Will add test soon.

Actually copyedited same logic from Uniscribe to make it just work