Process pixels in raster order

Process pixels in raster order

If we're imitating a CRT character generator, obviously we should
process pixels line-by-line, not column-by-column.  But that means
writing "for (y ...)" before "for (x ...)" which isn't the instinctive
way I did it.

So now that's corrected and the Y loops are outside the X loops, which
should make any debugging output easier to follow.  This has been
confirmed not to change FreeType rendering at 10.5 ppem.