Improve diff for assertCountEqual() to actually show the differing counts.

New output looks like this:

Traceback (most recent call last):
  File "test.py", line 5, in test_ce
    self.assertCountEqual('abracadabra xx', 'simsalabim xx')
AssertionError: Element counts were not equal:
Expected 5, got 2:  'a'
Expected 2, got 1:  'b'
Expected 0, got 2:  'i'
Expected 0, got 2:  'm'
Expected 0, got 1:  'l'
Expected 0, got 2:  's'
Expected 1, got 0:  'c'
Expected 1, got 0:  'd'
Expected 2, got 0:  'r'

Lib/unittest/test/test_assertions.py

@@ -229,12 +229,6 @@ def testAssertDictContainsSubset(self):
                              "^Missing: 'key'$",
                              "^Missing: 'key' : oops$"])
 
-    def testassertCountEqual(self):
-        self.assertMessages('assertCountEqual', ([], [None]),
-                            [r"\[None\]$", "^oops$",
-                             r"\[None\]$",
-                             r"\[None\] : oops$"])
-
     def testAssertMultiLineEqual(self):
         self.assertMessages('assertMultiLineEqual', ("", "foo"),
                             [r"\+ foo$", "^oops$",