Prompt user to continue when there is a uncommitted diff.

Review Request #4390 — Created Aug. 5, 2013 and discarded — Latest diff uploaded




Sometimes the user may forget to commit the change before putting a patch to revision, which end up being a empty revision, which is confusing.
This patch gives user a warning when there is a uncommitted diff by asking if he/she really wants to continue.
Test with both dirty branch and clean branch, works fine.