FIX: [MakeMaker] prerequisites in Makefile.PL

found while converting ExtUtils-Depends to dzil (I had to manually add some extra prereq declarations to work around these issues):

- the minimum perl requirement was only being extracted from the runtime and build phases; now also look in configure and test
- %FallbackPrereqs only contained prereqs from build, runtime and test (because that's the phases that were screwed up in older CPAN.pm); now also fold in prereqs from configure-requires -- these are the prereqs that are used when the user's ExtUtils::MakeMaker is really old.