Once we pick a license this might change, but
in the mean time, at least the NCSA UIUC origin is noted.

and let postdraw return an int.  Keep looping, re-rendering,
until postdraw returns zero.

so we can use same function for both.

have "o2w" transforms that are really interpreted relative to camera space.
Also start adding per-object clip support; this requires change to
subcameras, supplying projection parameters subc_lrbt()
rather than a (clip-dependent) projection matrix.