Add a warning when version is parsed as legacy

Define a __hash__ on the packaging.version.Version subclasses

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.

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.

Add more compatability shims to SetuptoolsVersion

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

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

Restore iterating over Version objects for compat with buildout

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