Users are prompted with the list of known changes we are about
to upload, and they can fill out the current change numbers for
any changes which already exist in the data store. For each of
those changes the change number and commit id is sent as part of
the upload request, so Gerrit can insert the new commit as a new
patch set of the existing change, rather than make a new change.
This facility permits developers to replace a patch so they can
address comments made on a prior version of the same change.
Signed-off-by: Shawn O. Pearce <sop@google.com>
