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.