Get rid of warnings from rspec-core's library and spec code.

[JonRowe]

Extension of #907 with some refactorings

[phiggins]

Heh, I figured somebody would know how to do this better than I could. Thanks for taking this to the finish line!

[JonRowe]

Not better, just different... my reasoning for pp is that I'd rather hide the warnings that pp generates, given it's a Ruby issue not an RSpec one rather than monkey patching the test. The other tweak is that warning's aren't necessarily enabled (although we do recommend them be on) so I'd rather preserve the original state afterwards.