BUG: the wrong executable was being found ...

... despite the right prefix being passed due to an embarrassing bug in
the code.
BUG: Do not remove site-packages even if it's empty.

pip and easy_install do not work, when site-packages directory is not
present.  Uninstalling a lone packages that was installed using
enstaller removes the site-packages directory, causing other tools to
not work.
Add a test which reproduces an infinite recursion in the case of cyclic dependencies.
Remove infinite recursion in case of dependancy cycles.
This patch is also an optimization in the case of highly connected acyclic graphs
Implement code review suggestions.
remove comment and fix typo
another typo :(
Make path checking more robust on windows.

Eliminates some useless warnings on Windows about PYTHONPATH.
DOC: Add auth info to proxy url in help and default enstaller4rc
REF: move default remote repository logic out of Enpkg.
BUG: hack to fix enstaller update logic.
BUG: update the version of enstaller.

It was not updated after 4.6.1 release.
BUG: fix -v option when arguments are given.
BUG: fix some version comparison special cases.
BUG: fix safe_write on windows when dst already exists.
ENH: use proper uri instead of hacked-up string manipulation for repos.

This allows us to fix quite a few windows test failures/errors.
BUG: fix uri_to_path and add tests.
BUG: fix tests to keep platform-specificities within platform guards.
ENH: Add a method to allow abortion of the fetching stage of actions.
Abort now allowed before every action, not just fetch.