They automatically git clone the original repository and execute the original script. So if they are first in the path, they will be executed. If a user has another git-cl/try in the path prior, these stubs won't be used at all and won't mess with the user's setup.

Also fix a bug with git handling in trychange.py
Review URL: http://codereview.chromium.org/119244

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@17737 0039d316-1c4b-4281-b951-d872f2087c98