merge: avoid to break the dirstate copy status on moved files

In the case a file is locally tracked as copied in dirstate, and that a merge
affects this file, this file should not be marked as modified in dirstate, as
this will break the current copy state.
Note: only affect working directory merge, not branch merge.

mercurial/merge.py

@@ -386,7 +386,8 b' def recordupdates(repo, action, branchme'
                 # of that file some time in the past. Thus our
                 # merge will appear as a normal local file
                 # modification.
-                repo.dirstate.normallookup(fd)
+                if f2 == fd: # file not locally copied/moved
+                    repo.dirstate.normallookup(fd)
                 if move:
                     repo.dirstate.forget(f)
         elif m == "d": # directory rename