py3: use list() to get a list of items using dict.items()

dict.items() on Python 3 returns a generator over the values of the dictionary,
hence we can't delete elements while iterating over dict.items() in Python 3.

Differential Revision: https://phab.mercurial-scm.org/D1799

mercurial/patch.py

@@ -2443,7 +2443,7 b' def diffhunks(repo, node1=None, node2=No'
     modified = sorted(modifiedset)
     added = sorted(addedset)
     removed = sorted(removedset)
-    for dst, src in copy.items():
+    for dst, src in list(copy.items()):
         if src not in ctx1:
             # Files merged in during a merge and then copied/renamed are
             # reported as copies. We want to show them in the diff as additions.