cache: fixes for GlyphIndex, FastIndex & FastGlyph

* update_process_glyph_fragments() ignored the text background rectangle

* moved the OpRight value fix-up to update_process_glyph_fragments() since
  it is required for all glyph primary drawing orders
Merge pull request #2257 from nfedera/fix-2014-12-05-01

cache: fixes for GlyphIndex, FastIndex & FastGlyph