#145 Blt can be the wrong one

[Paul F. Dubois]

When Python builds _tkinter, it looks to see if there
is a Blt build. In the setup.py for Python, there is a
'PCDMI' change block on this subject, although it looks
to me like it doesn't do what it says in the comment.

On a redhat system at LC, there is apparently a Blt out
there somewhere that gets found and it was not built
with the cdat versions of tcl/tk, so link errors occur.

I think the solution is to ALWAYS disallow Blt being
included, unless there is some pressing reason to have
it, in which case you'll need to add it to pysrc.