Fixes for argcomplete

- separate out most argcomplete related stuff in new file _argcomplete.py
  (could probably be in the py library)
- allow positional arguments to be interspaced with optional arguments
  ( + test in test_parseopt.py )
- removed double argument in tox.ini
- add documentation on installing argcomplete (>=0.5.7 as needed for
  Python 3), might need improving/incorporation in index.

This does not work on 2.5 yet. I have patches for argcomplete
(with/print()/"".format) but I am not sure they will be accepted.
Agreed with hpk not to push for that.

Removing argcomplete and leaving completion code active now works by early
exit, so <TAB> no longer re-runs the programs without parameters
(which took long for py.test)

test calls bash with a script that redirects filedescriptor 8 (as used by
argcomplete), so the result can be tested.

--HG--
branch : argcomplete

_pytest/_argcomplete.py

@@ -0,0 +1,68 @@
+
+"""allow bash-completion for argparse with argcomplete if installed
+needs argcomplete>=0.5.6 for python 3.2/3.3 (older versions fail
+to find the magic string, so _ARGCOMPLETE env. var is never set, and
+this does not need special code.
+
+argcomplete does not support python 2.5 (although the changes for that
+are minor).
+
+Function try_argcomplete(parser) should be called directly before
+the call to ArgumentParser.parse_args().
+
+The filescompleter is what you normally would use on the positional
+arguments specification, in order to get "dirname/" after "dirn<TAB>"
+instead of the default "dirname ":
+
+   optparser.add_argument(Config._file_or_dir, nargs='*'
+                               ).completer=filescompleter
+
+Other, application specific, completers should go in the file
+doing the add_argument calls as they need to be specified as .completer
+attributes as well. (If argcomplete is not installed, the function the
+attribute points to will not be used).
+
+---
+To include this support in another application that has setup.py generated
+scripts:
+- add the line:
+    # PYTHON_ARGCOMPLETE_OK
+  near the top of the main python entry point
+- include in the file calling parse_args():
+    from _argcomplete import try_argcomplete, filescompleter
+   , call try_argcomplete just before parse_args(), and optionally add
+   filescompleter to the positional arguments' add_argument()
+If things do not work right away:
+- switch on argcomplete debugging with (also helpful when doing custom
+  completers):
+    export _ARC_DEBUG=1
+- run:
+    python-argcomplete-check-easy-install-script $(which appname)
+    echo $?
+  will echo 0 if the magic line has been found, 1 if not
+- sometimes it helps to find early on errors using:
+    _ARGCOMPLETE=1 _ARC_DEBUG=1 appname
+  which should throw a KeyError: 'COMPLINE' (which is properly set by the
+  global argcomplete script).
+   
+"""
+
+import sys
+import os
+
+if os.environ.get('_ARGCOMPLETE'):
+    # argcomplete 0.5.6 is not compatible with python 2.5.6: print/with/format
+    if sys.version_info[:2] < (2, 6):
+        sys.exit(1)
+    try:
+        import argcomplete
+        import argcomplete.completers
+    except ImportError:
+        sys.exit(-1)
+    filescompleter = argcomplete.completers.FilesCompleter()
+
+    def try_argcomplete(parser):
+        argcomplete.autocomplete(parser)
+else:
+    def try_argcomplete(parser): pass
+    filescompleter = None