Add a PEP440Warning to make it easier to silence these warnings

Don't warn on empty non PEP 440 versions

Empty versions which are not PEP 440 are more likely to be the
fault of setuptools internals rather than anything a user has done
so these warnings are needless spam in that situation.

This fixes an error where there is a different result for if 2.0.5
is contained within >2.0dev and >2.0.dev even though normalization
rules should have made them equal.

In Python 3.x a subclass will not inherent the __hash__ method from
the parent classes if the subclass defines a __eq__ method. This
means that without defining our own __hash__ the SetuptoolsVersion
classes are unhashable.

* Enables indexing the SetuptoolsVersion objects, triggering the
  legacy behavior warning.
* Enables comparing the SetuptoolsVersion object to a tuple, again
  triggering the legacy behavior warning.

Now that pytest is invoked via setup.py, it should no longer be necessary to continue to support running tests via setup.py test.

Conflicts:
	.hgtags
	CHANGES.txt
	ez_setup.py
	setuptools.egg-info/requires.txt
	setuptools/version.py