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
Move unpack_url to pip.download

This puts all unpack functions in the same place.
Cherrypicked from a commit of qwcode
Align unpack_http_url to unpack_file_url
pip.download: add docstring and log
pip.download: refactor and try to clarify

add _check_download_dir and _download_http_url to ease the understanding
of unpack_http_url and unpack_file_url functions
Merge pull request #1822 from xavfernandez/develop_moveunpack

Move unpack_url to pip.download
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
Fixing issues with install's --target option.

 1. Check for the existence of a directory before copying from temporary directory to final target. If it exists, warn the user.
 2. If the user specifies the --upgrade option and the directory exists, delete it and continue with installation.
 3. Adding tests for above cases.

This resolves #1489, #1710 completely and parts of #1833.
Fixing pep8 errors
Merge pull request #2006 from dstufft/upgrade-six

Upgrade six to 1.7.3