ENH: use #!/usr/bin/env python for the shebang instead of non-working on POSIX systems plain #!python

Fix NameError during installation with Python implementations (e.g. Jython) not containing parser module.

ENH: use #!/usr/bin/env python for the shebang instead of non-working on POSIX systems plain #!python

Fixed tests for skipping when svn not present.

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extra : histedit_source : 6cd9a3c6003d3f6de2f8e676b61589db4dffafb0

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extra : histedit_source : 2f1f4146ec1d5196cb65602302185a12060cfa17

--HG--
extra : histedit_source : 7924e09d06d2f6db58371735314caeee77aa2d3d

--HG--
extra : histedit_source : 9a99f28235a96543a3ca2da4ec691da0e1cd880c

--HG--
extra : histedit_source : b0072af02db4ba170105a4eb3f8a033dce678869

--HG--
extra : histedit_source : 471b9c3fbde309c39492f2a567a26993c1dc94de

  setUp.
test_egg_info, test_sdist, and test_svn all had tests that needed to be
  bypassed when svn was not present.  tests.py26compat contains a SkipIf
  decorator for skipping.  This worked after ironing a few wrinkles.  The
  conditions is evaluated and stored in test_svn._svn_check.

--HG--
extra : amend_source : fe3ad40ffbb67cc7f3407a37ac42671ea3ecb983

Remove internal implementation of ImpImporter and ImpLoader as comments indicate they're only required for Python 2.4.