[pip/req] added _strip_postfix, _build_req_from_url, _build_editable_options. Not parse_editable returns package,url, options
[tests] added test for subdirectory editable options
[pip/req] editable_options defaults to None
Merge from upstream project
[docs/usage.rst] added example of subdirectory installation
Added subdirectory editable options changes to CHANGES.txt
Merge remote-tracking branch 'pip-orig/develop' into develop
Merge remote-tracking branch 'niedbalski/develop' into subdirectory-editable

Conflicts:
	CHANGES.txt
	tests/functional/test_install_reqs.py
	tests/lib/__init__.py
	tests/unit/test_req.py

Additional work - refactored tests to new style.
Fix deleted brack
Merge pull request #1215 from pnasrat/subdirectory-editable

Merge subdirectory editable feature