Message 243451 - Python tracker

I committed a presence test for Tix in #21337 that should catch problems with loading Tix after this patch.  There shouldn't be any problem though, we actually install Tix into Tcl/Tk whereas TIX_LIBRARY is (to my understanding) for helping Tcl/Tk find a Tix that it can't find itself.

Steve, I think I have BuildForRelease patched in properly; it works with BuildForRelease unset at least :)