Support automatically stashing local modifications during repo-rebase.

Currently repo-rebase requires that all modifications be committed
locally before it will allow the rebase. In high-velocity environments,
you may want to just pull in newer code without explicitly creating
local commits, which is typically achieved using git-stash.

If called with the --auto-stash command line argument, and it is
determined that the current index is dirty, the local modifications
are stashed, and the rebase continues.  If a stash was performed, that
stash is popped once the rebase completes.

Note that there is still a possibility that the git-stash pop will
result in a merge conflict.

Change-Id: Ibe3da96f0b4486cb7ce8d040639187e26501f6af
1 file changed