Corrected the run shell command test

Quote the file name given in the shell command, to avoid Windows separators be considered as escape characters.
shlex.quote was added in Python 3.3, so manually quote the test file name

... we want tests to pass in Python 2.6
In bundle.uninstall(), clean up the parent reference to the removed module

This avoids a KeyError in IronPython, as it might think the module is in sys.modules due to this reference.
Removed the unused shlex import
Skip the "threads" command test in interpreters which don't support it

 IronPython Jython, ...