Better commented the code, especially the result caching & lazy distribution
list sorting strategies implemented there. Added several TODO comments
indicating things to look into there in the future.

General code cleanup:
 - stopped reusing the project_name variable for different purposes
 - added an assertion to detect corrupt distribution list caches

--HG--
extra : source : 86ef8f59ef4e1fc253c155b9ca0856497455372d

--HG--
extra : source : 32166eed1174dc565d903c81b9d99c292357aecc

--HG--
extra : source : ab82442e2205a4ab1016711e482388590688fa15

Skip this test because it now fails under Python 3.3 and earlier apparently due to a bug in the inspect module. Since the test passes under Python 3.4 and later, that should still serve as a suitable regression test.

Extract the resolution of loader/runner classes. Allows None value to pass-through to unittest.main. Fixes #180.

Allow install to proceed with an egg install on IronPython and any other environment that has no stack support. Fixes #177.

--HG--
extra : amend_source : c92063405d99e7fdb7fe0a6312fa8438c3727c2f

--HG--
extra : amend_source : 829ebde0696d12adfb54aca74ea6b1b510177ff4

--HG--
extra : amend_source : 62f689b409b4645eda5f81b2604c50a84713ee52

Removed notice about PEP 420 package finder. Discussion in the ticket (Ref #97) indicates that the implementation is currently inadequate.