Removed `vary_delim_re` in `django/utils/cache.py` in favor of existing...

Removed `vary_delim_re` in `django/utils/cache.py` in favor of existing `cc_delim_re` since the latter is more correct in parsing the header (allows whitespace before and after comma separators instead of just after).  As a bonus, tests added for `patch_vary_headers()`.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@6696 bcc190cf-cafb-0310-a4f2-bffc1f526a37