disambiguate branches from filenames in ggc
remove outdated `git branches-behind` script

“fixes” #26
add 'grep' dir to PATH
many copy-diffs{,-test,-script} improvements

- timestamps on many log statements
- remove untracked files that are not / no longer present in the source
  repo
- remove files under .git in the destination that are not present in the
  source repo’s .git
  - this, for example, clears out deleted branch refs from the
    destination repo
- fire on changes to untracked (but not .gitignore’d) files; complete
  treating untracked-but-not-gitignored files as 1st-class citizens when
  copy-diff’ing
- verify that some commands give equal output on the source and dest
  repos when `copy-diffs` is finished:
  - git diff
  - git diff —cached
  - git lso  # list untracked files
- handle the situation where `watchman` was started without the $USER’s
  full $PATH, e.g. by `launchd` on OSX.
`new-branch` uses origin/HEAD, not origin/master
skip cleaning up test files if env var is set

useful for debugging tests
change to original git repo when cleaning up tests

copy-diffs-test creates clones of itself in subdirs, so `git root` only
takes you to their roots, which is not where you want to run the
clean-test-files script.
add copy-diffs-test to run-tests script

it was mistakenly left out