[1.6.x] Fixed #15625 -- Made message in MultiValueDictKeyError less verbose.

Thanks margieroginski for the suggestion.

Backport of 893198509e from master

django/utils/datastructures.py

@@ -298,7 +298,7 @@ class MultiValueDict(dict):
         try:
             list_ = super(MultiValueDict, self).__getitem__(key)
         except KeyError:
-            raise MultiValueDictKeyError("Key %r not found in %r" % (key, self))
+            raise MultiValueDictKeyError(repr(key))
         try:
             return list_[-1]
         except IndexError:

tests/utils_tests/test_datastructures.py

@@ -234,11 +234,7 @@ class MultiValueDictTests(SimpleTestCase):
                           [('name', ['Adrian', 'Simon']),
                            ('position', ['Developer'])])
 
-        # MultiValueDictKeyError: "Key 'lastname' not found in
-        # <MultiValueDict: {'position': ['Developer'],
-        #                   'name': ['Adrian', 'Simon']}>"
-        six.assertRaisesRegex(self, MultiValueDictKeyError,
-            r'"Key \'lastname\' not found in <MultiValueDict',
+        six.assertRaisesRegex(self, MultiValueDictKeyError, 'lastname',
             d.__getitem__, 'lastname')
 
         self.assertEqual(d.get('lastname'), None)