revert: make backup when unforgetting a file (issue3423)

This skips the backup if it would be a duplicate.

mercurial/cmdutil.py

@@ -1976,7 +1976,7 b' def revert(ui, repo, ctx, parents, *pats'
             #   make backup if not in target manifest
             (modified, revert, remove, True, True),
             (added, revert, remove, True, False),
-            (removed, undelete, None, False, False),
+            (removed, undelete, None, True, False),
             (deleted, revert, remove, False, False),
             )
 
@@ -1986,7 +1986,8 b' def revert(ui, repo, ctx, parents, *pats'
             def handle(xlist, dobackup):
                 xlist[0].append(abs)
                 if (dobackup and not opts.get('no_backup') and
-                    os.path.lexists(target)):
+                    os.path.lexists(target) and
+                    repo[None][abs].cmp(ctx[abs])):
                     bakname = "%s.orig" % rel
                     ui.note(_('saving current version of %s as %s\n') %
                             (rel, bakname))

tests/test-issue660.t

@@ -73,6 +73,15 b' Revert all - should succeed:'
 
   $ hg st
 
+Issue3423:
+
+  $ hg forget a
+  $ echo zed > a
+  $ hg revert a
+  $ hg st
+  ? a.orig
+  $ rm a.orig
+
 addremove:
 
   $ rm -r a b