Increase precision for B/W rasterizer.

* src/raster/ftraster.c (Set_High_Precision): Add two more bits to
the precision.  This corrects rendering of some small glyphs, for
example, glyph `xi' in verdana.ttf at 13 ppem.  Testing with ftbench
on my GNU/Linux box I don't see a performance degradation.
2 files changed