Fixed #5981 -- Fixed failing regression test when using locmem cache backend.  Changed `add` to pickle the value as is done in `set`.  Based on patch from mattmcc.
Fixed #5981 -- Fixed failing regression test when using locmem cache backend.  Changed `add` to pickle the value as is done in `set`.  Based on patch from mattmcc.

--HG--
extra : convert_revision : svn%3Abcc190cf-cafb-0310-a4f2-bffc1f526a37/django/trunk%406709

adieu/django-nonrel,adieu/django-nonrel,adieu/django-nonrel