mutually exclusive group stops working when specified via parent parser about argparse HOT 5 CLOSED

I've attached argparse-0040-add-parents-mutex-groups.patch which fixes the 
problem.

Steven, is there a more correct way to fix it? 

If my understanding of argparse is not too far of the track I could add some 
tests of
mutex groups added via parents for the next bug-fix release.

That looks like about the right way to fix it to me. I've committed a variant 
of your
patch along with a test in r45.

I've added some tests on top of r47 version.
The attached argparse-0047-mutex-tests.patch adds to test/test_argparse.py 
tests for
mutex groups.

Great, thank you for the extra tests! Added in r49.