* `git bash` helper now will either:
    * launch an interactive bash prompt in the MinGW Terminal Emulator
    * launch a non-interactive bash shell if arguments are provided
  * `git bash` now includes python, python/Scripts and svn binaries in
    the PATH.
  * depot_tools' colorization now works in MinGW Terminal Emulator
  * batch scripts are now regenerated if any of them is missing.

R=agable@chromium.org, dnj@chromium.org, mmoss@chromium.org
BUG=598956

Review URL: https://codereview.chromium.org/1847783002 .

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@299616 0039d316-1c4b-4281-b951-d872f2087c98