There are still texture sampling issues that I don't understand. Until
I properly understand this, using (bitmap) fonts that have
power-of-two dimensions seem to produce "acceptable but incorrect"
results.
This fully threads both the real minimum size of the texture and the
dimensions of the texture through to the TA parameters.
This also removes spurious zero-area drawing commands (space
characters).
This still needs to be cleaned up, particularly to properly pass the
texture size around--there are a few unnecessary '128x256' magic
numbers scattered in the code.
