Add Python 3 support to the Python test.py script.

The print function is used in place of the print statement.

The urlopen function has been moved to urllib.request in Python 3, so
attempt to import it from either location.

TestCase.assert_() has been deprecated in place of
TestCase.assertTrue().

The tests all pass in both Python 2 and 3.

Also, removed the one from modules/python/src2/cv.py and cleared its
executable bit, since it's not a script.

Use github pat to get data for in python tests (files from code.opencv.org are received truncated sometimes)

updated some more links

updated links in cheatsheet
renamed directory for Mat tutorial 
changed links from willow docs to opencv.itseez.com, from Trac to current Redmine

disable implicit numpy array use in old-style Python bindings because of hard-to-fix memory leaks (ticket #1177)

extended cv.KMeans2 API in Python (ticket #414; thanks to hogelog). fixed failures in the opencv python tests.