#72 Shaded transparency works incorrectly at strange sizes

[Tony]

When the size of a pseudo-transparent, shaded aterm in
CHARACTERS doesn't quite fill the size of the aterm in
PIXELS -- when the dimensions of the font don't divide
evenly into the size of the terminal, the transparency
for the extra space is wrong. The background data for
that area seems to be taken from the opposite edge of
the terminal.

Screenshot attached.

Note that this only occurs when shading is on, and that
pixmap backgrounds don't appear to be affected by it.

[Tony]