Display versions of uninstalled distributions

It's helpful to see the versions uninstalled for auditing purposes and
if the user realizes they broke something and they want to restore
things back to exactly how they were.

Before:

    $ pip uninstall pyrepl pytest
    Uninstalling pyrepl:
      Successfully uninstalled pyrepl
    Uninstalling pytest:
      Successfully uninstalled pytest

After:

    $ pip uninstall pyrepl pytest
    Uninstalling pyrepl 0.8.4:
      Successfully uninstalled pyrepl 0.8.4
    Uninstalling pytest 2.6.4:
      Successfully uninstalled pytest 2.6.4
Good points. I'll change it to be explicit and I'll merge the 2 PRs so we have consistency and less moving parts.