[1.2.X] Fixed #13007 -- Made cookie parsing resilent to the presence of...

[1.2.X] Fixed #13007 -- Made cookie parsing resilent to the presence of cookies with invalid characters in their names. Thanks Warlax for the report, Ubercore for his work on a fix and Jannis and Luke for review and guidance.

Backport of [15523] from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@15524 bcc190cf-cafb-0310-a4f2-bffc1f526a37