Rationalised CompatCookie/SimpleCookie into single SimpleCookie class with all fixes.

      Since upstream Python has fixed the encoding bug (see
http://bugs.python.org/issue9824), we don't want a separate class for this
bug fix, or several layers for the different fixes.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15298 bcc190cf-cafb-0310-a4f2-bffc1f526a37