Check for Jython using sys.platform, not os.name

Partial appears to behave differently on Python 2.6. Also, this syntax is more congruent and easier to read.

Fix TypeError for pytest.skip()

pytests skip() method doesn't have a 'reason' parameter.
This fixes:

  TypeError: skip() got an unexpected keyword argument 'reason'

--HG--
branch : fix-type-error-skip-reason

--HG--
branch : fix-type-error-skip-reason

It fixes failure of setuptools.tests.test_sandbox.TestSandbox.test_setup_py_with_CRLF() with Python 3.1.

DistributionNotFound: Show requirers

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branch : DistributionNotFound_list_requirers

Disable warning of LegacyVersion in parsed_version. This functionality should be called explicitly at whatever times are appropriate for the warning. Fixes #307.