Integrate changelist 6122 from //guest/dimitry_andric/revml/branch/5088:
Handle the case where the Perforce server decides to rename the
changelist number at the last instant of a submit (usually due to a
busy queue of incoming requests).
This fix does a bit stricter matching on the "Change NNNN submitted"
line output by the p4 command, and handles the "Change NNNN renamed
change MMMM and submitted" line properly, by picking up number MMMM
instead of NNNN.