This changeset:

http://hg.python.org/cpython/rev/c3fb79d1c036

breaks nose, as it changes the behavior of unittest.TestProgram in a
non-backwards-compatible way. Previously, when called like:

TestProgram(testRunner=None)

self.testRunner would be None when runTests() was called. Now, it is 
populated with the default TextTestRunner class in TestProgram.__init__. 
nose expects self.testRunner to be None or a runner instance in 
runTests(), and thus fails immediately with 2.6.3.

If initialization of self.testRunner could be deferred to runTests() as 
in unitttest for 2.5 and earlier, that would be ideal for nose.