update help to make Package Index Options' usage clearer, ref #1814
Optional finder variable must be validated before use
detect windows when running under IronPython
fixed windows test
Replaces spaces in username.

Conflicts:
	pip/locations.py
Merge pull request #1897 from paweljasinski/ironpython

detect windows when running under IronPython
Merge pull request #1815 from pcx/develop

update help to make Package Index Options' usage clearer, ref #1814
Fix to add a missed/new windows compat location
Merge pull request #2004 from dstufft/use-windows-compat-check

Fix to add a missed/new windows compat location
Test that parse_requirements does not require a finder
Merge pull request #2005 from dstufft/pr-1959

Continue PR #1959
Upgrade six to 1.7.3
Merge pull request #2006 from dstufft/upgrade-six

Upgrade six to 1.7.3
Fix --no-cache-dir
Merge pull request #2010 from dstufft/fix-no-cache

Fix --no-cache-dir
docs: there are also independent package managers
Merge pull request #2015 from techtonik/patch-3

docs: there are also independent package managers