Picked packages are reported in lowercase.

Packages in the version list are already case-insensitive, but when a
package like 'Sphinx' or 'Django' is picked, the reported version pin
still looked like 'Django = 1.4.3'. To make sorting easier and to
prevent confusion, 'django = 1.4.3', all lowercase, is better.

The only place where the "real" case is reported is somewhere in the
setuptools dist matching where the dist is printed directly. I
haven't put a `str(dist).lower()` around that, it seemed pretty internal.

Note: I'd consider this to be a new feature, not a bugfix. As such it is not for 2.0.1/2.0.2, but for 2.1.

Suggested changelog entry: "Picked packages are reported in lowercase now."