Enable testing on more Python versions and PyPy

… except for the refcount test which doesn't work (and makes no sense)
under PyPy as it has a non-reference count model).
Unify env and python variable TEST_DIR

The difference is just confusing.
Fix copyright years and intent to (not) test Solaris
Fix homepage URL
Fix some indentation issues in tests
Bump version for a trivial 0.5.2 release
Add a 'dist' target