Make Makefile.PL less irritating.

Make Makefile.PL less irritating.

Complain about all the Module::Install extensions in one go.
Do all the author_requires in another go.

This means that if you've got a clean-ish machine, you only get two
irritating lists to feed to cpanm, rather than having to do an
irritating install, perl Makefile.PL, install cycle till it works.

Also fix use of M::I extensions to include parens, as otherwise
if they're not installed then M::I doesn't load them, and our requires
checking is now at runtime rather than compile time (and 5.16.0
doesn't like it at compile time)..