Ezio, you brought up the fact that the 2.7 Windows buildbots were skipping the Tkinter tests in Terry's core-mentorship thread about tkinter on Windows last month, and I've finally learned what is causing that failure.  It appears that when 689a813f4afc and df39b0bc4106 were committed, they were not backported to 2.7.  Attached is a patch to backport those two changesets, which should make things (more) right.  

This only affects running tests via PCbuild/rt.bat (or Tools/buildbot/test.bat, which calls PCbuild/rt.bat), and doesn't do anything for finding the tcl/tk .dlls any other time.