Fix pep8 issue
Bump version for development of 6.0.2
Update installing.rst

Resolve merge conflict on updating on Windows.
Add PEP 440 to the change log
Don't return cached output for InstallRequirement().installed_version
Bump for release of 6.0.2
Merge branch 'release/6.0.2'
Merge branch 'master' into develop

Conflicts:
	CHANGES.txt
	pip/__init__.py
Merge branch 'develop' of github.com:pypa/pip into develop