copies: switch to using pathutil.dirname

copies had it's own dirname implementation. Now that pathutils has a common one,
let's use that instead.

mercurial/copies.py

@@ -5,15 +5,9 b''
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
-import util
+import util, pathutil
 import heapq
 
-def _dirname(f):
-    s = f.rfind("/")
-    if s == -1:
-        return ""
-    return f[:s]
-
 def _findlimit(repo, a, b):
     """
     Find the last revision that needs to be checked to ensure that a full
@@ -384,7 +378,7 b' def mergecopies(repo, c1, c2, ca):'
     # examine each file copy for a potential directory move, which is
     # when all the files in a directory are moved to a new directory
     for dst, src in fullcopy.iteritems():
-        dsrc, ddst = _dirname(src), _dirname(dst)
+        dsrc, ddst = pathutil.dirname(src), pathutil.dirname(dst)
         if dsrc in invalid:
             # already seen to be uninteresting
             continue