Special case os.devnull for PIP_CONFIG_FILE to mean 'no config file'
Merge pull request #1544 from pfmoore/devnull

Special case os.devnull for PIP_CONFIG_FILE to mean 'no config file'
'pip wheel' should download wheels, when it finds them

Conflicts:
	pip/commands/wheel.py
	pip/download.py
	pip/req/req_set.py
	pip/wheel.py
when file urls have hash fragments, check it
fixes for downloading wheels (Issue #1112)

Conflicts:
	pip/req/req_set.py
cherry-pick fixes
update changelog
pip docs refactor
Ensure wheel-Version is compatible with pip
Fix tests to expect installation or not
Explain futurewheel version numbers
deprecate --build and --no-clean
Merge pull request #1574 from qwcode/deprecate_build

deprecate --build and --no-clean
Small cleanup, use email.parser.Parser
Merge branch 'develop' of https://github.com/pypa/pip into test-wheel-version
Use find_on_path, extract compatibility check
Add unit test for check_compatibility
Python 3 compatibility
Remove commented line
Fix test logic, tiny error / import cleanup