cmdutil: add copy-filtering support to duplicatecopies

In order to fix issue 4192 we need to be able to skip some copies
while doing duplicatecopies.

mercurial/cmdutil.py

@@ -1913,11 +1913,22 b' def cat(ui, repo, ctx, matcher, prefix, '
 
     return err
 
-def duplicatecopies(repo, rev, fromrev):
-    '''reproduce copies from fromrev to rev in the dirstate'''
+def duplicatecopies(repo, rev, fromrev, skiprev=None):
+    '''reproduce copies from fromrev to rev in the dirstate
+
+    If skiprev is specified, it's a revision that should be used to
+    filter copy records. Any copies that occur between fromrev and
+    skiprev will not be duplicated, even if they appear in the set of
+    copies between fromrev and rev.
+    '''
+    exclude = {}
+    if skiprev is not None:
+        exclude = copies.pathcopies(repo[fromrev], repo[skiprev])
     for dst, src in copies.pathcopies(repo[fromrev], repo[rev]).iteritems():
         # copies.pathcopies returns backward renames, so dst might not
         # actually be in the dirstate
+        if dst in exclude:
+            continue
         if repo.dirstate[dst] in "nma":
             repo.dirstate.copy(src, dst)