Fix freetype2 include directory not being added to CFLAGS

See https://github.com/facebook/hhvm/issues/1380
Install hhvm in the Cellar
Merge pull request #23 from mcuelenaere/fixes

Fix freetype2 include directory + install hhvm in Cellar
Merge remote-tracking branch 'upstream/master' into brew_prefix

Conflicts:
	Formula/hhvm.rb