findcopies: fix rename bug

We've fiddled with this line several times, and an old bug has
reappeared from it. Let's take a peek at the history.

The original "or" (rev 3674, in 0.9.2 and 0.9.3):
  http://www.selenic.com/hg/rev/9103dab96093

Then I changed it to an "and" to fix a bug (rev 4304):
  http://www.selenic.com/hg/rev/4787e2b0dd03

Then for reasons now lost in the mists of time, I dropped half (rev 4399):
  http://www.selenic.com/hg/rev/93652499bed3

Then we added back the "or" (rev 4416, in 0.9.4):
  http://www.selenic.com/hg/rev/bb1800a7d7e1

So it seems it ought to be "and".

mercurial/merge.py

@@ -180,7 +180,7 b' def findcopies(repo, m1, m2, ma, limit):'
                 continue
             # named changed on only one side?
             if ca.path() == c.path() or ca.path() == c2.path():
-                if c == ca or c2 == ca: # no merge needed, ignore copy
+                if c == ca and c2 == ca: # no merge needed, ignore copy
                     continue
                 copy[c.path()] = of
 
@@ -280,7 +280,7 b' def findcopies(repo, m1, m2, ma, limit):'
 
 def symmetricdifference(repo, rev1, rev2):
     """symmetric difference of the sets of ancestors of rev1 and rev2
-    
+
     I.e. revisions that are ancestors of rev1 or rev2, but not both.
     """
     # basic idea: