warn the user about an old [MakeMaker::Awesome]

Dist::Zilla 5.020 broke [MakeMaker::Awesome] ($eumm_version became undef); version 0.22 fixes that.  These changes add x_breaks metadata, and a t/zzz-check-breaks.t that checks that data, as well as looking at the conflict information prepared by Moose::Conflicts.  This test never fails; it only diag()s noisily when it finds something.