check-code now handles 3 main use cases:
check-code report: Generate a report of pep8, pep257, and pyflakes problems
check-code regression: Diff said report from current ref to the upstream git ref
check-code junit: Create a junit report of all problems in the current git ref
Additionally:
* You can specify which files to check (check-code junit r2/r2/models/link.py)
* You can send output to a file (check-code -O junit.xml junit)
This script will determine if changes from the upstream branch to the
current branch have caused any additional reports from pep8, pep257, and
pyflakes.
