Bug 682421 - Arabic is broken with gravity hint=line when gravity is east/north
Bug 682421 - Arabic is broken with gravity hint=line when gravity is east/north

Fix-up gravity and vertical support in HarfBuzz module.

Still needs more work for vertical GPOS to work correctly, but this is a
huge improvement already.

kari-lentz/alpha-pango,Distrotech/pango,danny-ku/pango,kari-lentz/alpha-pango,Distrotech/pango,Distrotech/pango,kari-lentz/alpha-pango,danny-ku/pango,danny-ku/pango,kari-lentz/alpha-pango