Cursor-extension bug?

There is a bug in some X servers, in how they handle pixmap cursors
created with a mask of None.

I'd be interested if people could test to see how widespread this is.
I've written a tiny little test program; see
ftp.rodents-montreal.org:/mouse/misc/cursor-bug.c for more (the header
comment elaborates).

I suspect this is present upstream; I've seen it on Linux as well as
NetBSD.  If it's still present and people think it's worth doing, I can
write a PR for it.

/~\ The ASCII				  Mouse
\ / Ribbon Campaign
 X  Against HTML		[email protected]
/ \ Email!	     7D C8 61 52 5D E7 2D 39  4E F1 31 3E E8 B3 27 4B