Fix failing tests in geo

[reidpr]

After upgrade to Python 3, some tests in geo are failing. Specifically:

• geo.gmm.gmm_fit_log_heuristic(): the last test in this method returns 2 components when 3 are expected. Fix and re-enable test.
• optimize.py has several issues related to TypeError: unorderable types: dict() < dict()

These tests have been disabled for now. The task is to fix the issue and re-enable the tests by changing testable.manualonly_register() to register() or removing the # doctest: +SKIP comment.