[Module-build-general] PATCH: make purge/remove Makefile

[Brian I. <in...@tt...>]

Here's another patch. I *always* use 'make purge' and I miss it in M::B
so I'm suggesting adding it. Very small change.

I also noticed you weren't deleting the Makefile; a task that any
self-respecting realclean is expected to do :)

Cheers, Brian