This change adds the option to use the current issue number, if any,
when doing a git cl patch. Instead of doing git cl issue (copy the
number) git cl patch <number>, one can simply do git cl patch -i

BUG=

Review URL: https://codereview.chromium.org/1641903002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@298582 0039d316-1c4b-4281-b951-d872f2087c98