Merged revisions 83675 via svnmerge from

Merged revisions 83675 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/branches/py3k

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  r83675 | r.david.murray | 2010-08-03 13:56:09 -0400 (Tue, 03 Aug 2010) | 12 lines

  #9444: use first of prefix_chars for help opt instead of raising error

  An argparse option parser created with a prefix_chars that did not
  include a '-' would happily add -h and --help options, and then throw
  an error when it tried to format the help because the - was an invalid
  prefix character.  This patch makes it use the first character of
  prefix_chars as the character for the help options if and only if '-'
  is not one of the valid prefix_chars.

  Fix by Theodore Turocy, unit tests by Catherine Devlin.
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