Warn when git cl upload might be overwriting a newer patchset.

git_cl.py

Index: git_cl.py
diff --git a/git_cl.py b/git_cl.py
index 2fd5d852f15d892dc6ae968fbd2ceee33cdb4666..fbb327338b2fc6884ca1b2e1a53446fac057ce9f 100755
--- a/git_cl.py
+++ b/git_cl.py
@@ -1285,6 +1285,15 @@ def CMDupload(parser, args):
     if not options.reviewers and hook_results.reviewers:
       options.reviewers = hook_results.reviewers
 
+  if cl.GetIssue():
+    latest_patchset = cl.GetMostRecentPatchset(cl.GetIssue())
+    local_patchset = cl.GetPatchset()
+    if local_patchset < latest_patchset:

[M-A Ruel, 2013/03/19 01:26:45]

The problem here is that you are comparing patchset ids and not patchset
numbers, and the ids are not guaranteed to be monotonically increasing.

[koz (OOO until 15th September), 2013/03/19 01:29:16]

Oh, they aren't? What if we change '<' to '!=' then, so the warning becomes
about uploading a change to an issue that has been uploaded to from somewhere
else (which is probably basically the same warning).

[M-A Ruel, 2013/04/02 20:08:54]

Yes please do.

[koz (OOO until 15th September), 2013/04/02 20:40:04]

Done.

+      print ('The last upload made from this repository was patchset #%d but '
+            'the most recent patchset on the server is #%d.'
+            % (local_patchset, latest_patchset))
+      ask_for_data('About to upload; enter to confirm.')
+
   print_stats(options.similarity, options.find_copies, args)
   if settings.GetIsGerrit():
     return GerritUpload(options, args, cl)