BUG: Fix packaging of libtk8.6.dylib on MacOSX. Fixes 0003822

This commit fixes a regression introduced by r23613 (attempts to
address 0003809 by updating tcl version)

Tk 8.6 build system has a known problem building the tk shared library.
To ensure fixup_bundle properly process the _tkinter.so python module,
we implemented the following workaround to fix the library id.
For more details
http://sourceforge.net/p/tcl/mailman/message/30354096/
http://na-mic.org/Mantis/view.php?id=3822

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23667 3bd1e089-480b-0410-8dfb-8563597acbee