Issue #13540: Expanded argparse documents to clarify the action API

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Issue #13540: Removed redundant documentation about Action instance attributes. Updated example and documentation per recommendations by Steven Bethard in msg149524.

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branch : 2.7
Issue #19612: subprocess.communicate() now also ignores EINVAL when using at
least two pipes.

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branch : 2.7
Issue #21591: Handle exec backwards compatibility in the AST builder.

Instead of deferring until runtime. This makes sure we hit the right
conditions in dealing with unqualified exec statements.

Reviewed by Victor Stinner. Test follows in a later commit.

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branch : 2.7
extra : rebase_source : a6c5934392c8046e66f4abd5d2781e61db7cea0b
Issue #21591: add test for qualified exec in tuple form.

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branch : 2.7
extra : rebase_source : daaa277baf9d24e60061a6930ce264125a5658ca
Issue #22023: Fix %S, %R and %V formats of PyUnicode_FromFormat().

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branch : 2.7
Issue #21951: Temporary skip crashing test_user_command on AIX.

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branch : 2.7
Issue #22068: Don't create self reference cycles in idlelib.ConfigDialog.
In 2.7, these become leaks and cause test_gc to fail.

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branch : 2.7
Issue #21580: Now Tkinter correctly handles binary "data" and "maskdata"
configure options of tkinter.PhotoImage.

Added private Tkapp method _createbytearray().

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branch : 2.7
 - update config.guess and config.sub to support openrisc.

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Fix typo in comment.

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Issue #13540: Update references to Action class to match syntax used for other classes in this file.

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Issue #13540: Merge commits

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branch : 2.7