Move from base.pm to parent.pm

This is the patch I have [submitted it to the Moose mailing list](http://www.nntp.perl.org/group/perl.moose/2012/09/msg2498.html) almost one year ago. Unfortunately nobody applied it at the time.

Now that the main development moved to Github, here is a pull request for that work rebased on the current master.
In addtion to the benefits for Moose and the global Perl ecosystem, this should help to fix the recently reported issue in `base.pm` : [perl RT #118561](https://rt.perl.org/rt3/Ticket/Display.html?id=118561). 

Cc: @stevan