Created --autoimport parameter to autoimport indicated dependencies.

[facundobatista]

This is done by passing a temp file that does the importing, then leaving the user in the interactive interpreter.

Changing PYTHONPATH was explored, but it was too difficult because a) needing to support current PYTHONPATH setting, and b) ipython does not respect that envvar.

Of course, there's no collision for -i because the fades is call is without script at all, this is enabled only for the interactive interpreter case.

While doing this, I also improved a little the "package names db" and its usage, as I needed the "reverse case" of it.

Also, changed my mind about doing this by default, as I proved more "hacky" than I expected. It's not important, though, if you want to always have it enabled, you can use --autoimport in your user's config.

[coveralls]

Coverage increased (+0.06%) to 81.748% when pulling 2190a83 on autoimport into 57f77b8 on master.