breakage from r99712

[Jack Howarth]

Joshua,
    Do you realize that https://trac.macports.org/changeset/99712 broke all
tcl/tk software that uses software like blt which uses fork() without exec()
like blt...

http://lists.macosforge.org/pipermail/macports-tickets/2012-July/115001.html

If you are going to make a rash change like this, please warn the other
developers so we can attempt to limit the breakage in our packages.
          Jack