- fixed handling of import from __future__
- self-tested and added own requirements.txt
- cleaned up usage to require a file or directory to scan (rather than
  defaulting to ".")
- vendored code from pip 1.6dev which fixes bug in search_packages_info
  until pip 1.6 is released
add missing file
- corrected version of vendored search_packages_info() from pip
- handle relative imports