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This patch permits the mixing of optionals with positionals, with the caveat that a particular positional cannot be split up.
If:
 parser = ArgumentParser()
 parser.add_argument('-f','--foo')
 parser.add_argument('cmd')
 parser.add_argument('rest', nargs='*')
 '-f1 cmd 1 2 3', 
 'cmd -f1 1 2 3', 
 'cmd 1 2 3 -f1' 
all give {cmd='cmd', rest=['1','2','3'], foo='1'}. 
But 'cmd 1 -f1 2 3', does not recognize ['2','3'].
Previously 'cmd -f1 1 2 3' would return rest=[], and not recognize ['1','2','3']. With this change the nargs='*' behaves more like nargs='+', surviving to parse the 2nd group of positional strings.
The trick is to modify arg_counts in consume_positionals(), removing matches that don't do anything (don't consume argument strings). 
 if 'O' in arg_strings_pattern[start_index:]:
 # if there is an optional after this, remove
 # 'empty' positionals from the current match
 while len(arg_counts)>1 and arg_counts[-1]==0:
 arg_counts = arg_counts[:-1]
This change passes all of the existing test_argparse.py tests. It also passes the optparse tests that I added in http://bugs.python.org/issue9334#msg184987
I added 4 cases to illustrate this change.