Fixed edge case that breaks the test suite on versions of Python > 2.6.4

Before http://svn.python.org/view?view=rev&revision=74647 it was possible to
pass a SimpleCookie to load, but this no longer works due to a different bug
in Python the said revision fixed.

My guess is a SimpleCookie was never intended to be passed through load which
is perfectly reasonable.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@11820 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/http/__init__.py

@@ -1,6 +1,6 @@
 import os
 import re
-from Cookie import SimpleCookie, CookieError
+from Cookie import BaseCookie, SimpleCookie, CookieError
 from pprint import pformat
 from urllib import urlencode
 from urlparse import urljoin
@@ -251,13 +251,15 @@ class QueryDict(MultiValueDict):
 def parse_cookie(cookie):
     if cookie == '':
         return {}
-    try:
-        c = SimpleCookie()
-        c.load(cookie)
-    except CookieError:
-        # Invalid cookie
-        return {}
-
+    if not isinstance(cookie, BaseCookie):
+        try:
+            c = SimpleCookie()
+            c.load(cookie)
+        except CookieError:
+            # Invalid cookie
+            return {}
+    else:
+        c = cookie
     cookiedict = {}
     for key in c.keys():
         cookiedict[key] = c.get(key).value