The following sequence:

 [ bind pixmap to texture ]
 XFreePixmap(dpy, pixmap);
 glGetTexImage(texture)

Reliably crashes the X server for me with AIGLX and the current zero-copy 
texture-from-pixmap code.

I haven't investigated the code in detail to figure out why this is
happening, but I assume either the code needs to reference the Pixmap
object until the binding is released (like SetWindowBackgroundPixmap),
or there needs to be a cleanup when the pixmap is freed.