Merge pull request #687 from dstufft/dont-import-site

Don't import site when executing with -p
(cherry picked from commit eb88e8f7b20b5d0809013100dc14fe2ebbf738da)
Merge pull request #688 from dstufft/upgrade-pip

Upgrade pip to 6.0.3
(cherry picked from commit 462ce30e7310dc43d55af18170761ff52204c4f8)
Merge branch 'release/12.0.3'
bump version for release
Merge branch 'master' into develop

Conflicts:
	docs/changes.rst
	virtualenv.py