The imagen itself is buggy as ----, and as a result this filter has to do a lot
of work to kluge around them. The imagen is our primary hardcopy device and so
this filter should pretty well be completely debugged by now.

One thing I can't get around: if you have overlay=no, vectors near the
edge of a raster block can get erased. This is because the imagen can't
arbitrarily position raster. Imagraster makes it look like the imagen
CAN arbitrarily position raster, but at the expense of adding
background-colored padding around the desired raster as necessary.

- Joe Dellinger
