Fixed our SimpleCookie overriding and use to be compatible with a (potential) stdlib SimpleCookie that fixes http://bugs.python.org/issue2193

The previous code tested the stdlib in a way that would always fail. It then
used an overridden SimpleCookie.load method that wouldn't work for the
stdlib. And it did some completely unnecessary monkey patching.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@16485 bcc190cf-cafb-0310-a4f2-bffc1f526a37