fix uninstall-from-outside-editable test; some hg versions can't clone into existing dir. Thanks Dave Abrahams.

fix test runner to operate fully within no-site-packages virtualenv; thanks Dave Abrahams for initial patch

Fixed #32 - Don't force a checkout after cloning a Git repository if the detected "revision" is the default.

Fixed #43 - Make sure we can install from directories directly (e.g. pip install path/to/dir/with/package).

Overwrite the local log file in ~/.pip/pip.log instead of appending to prevent huge log files. For a verbose log file use the --log option explicitely (which will be appended to).

Be a little quieter when using an already activated virtualenv to be able to have clean freeze entries.

Fixed #66 - Don't create a working copy after cloning a Mercurial repo because there an explicit update happens after that anyway. Thanks for the tip, Dirkjan Ochtman.

factor out get_installed_distributions utility function and add pip uninstall autocomplete; fixes #76