Normalize distribution and release data

This is a feature I need for Gitpan.  It lets you fix distribution names and release data.

I have it on by default because I see the primary purpose of BackPAN::Index is to provide a human-useful view of the history of distributions complete with corrections we've learned.  OTOH having it off by default serves the use case of BackPAN::Index as an precise reproduction of what is on BackPAN.

On by default is also a bit less backwards compatible, so there's that.

I only have a bit of normalization data in there right now.  I will surely find more when I crank over Gitpan again.