Remove unused imports
Clean up imports in package_index
Re-indent several function signatures to reduce linter warnings
Normalize whitespace in package_index.py
Replace import * with explicit imports, allowing linter to detect the missing imports reported in #53.
Add 'urlsplit' and 'urlunsplit' to compat module
Import urlsplit and urlunsplit from compat module. Fixes #53.
Make PackageIndex._vcs_split_rev_from_url a static method (as it doesn't have any instance or class references).
Add test to exercise the basic functionality of _vcs_split_rev_from_url