Fixed #12195 -- Clarified cache documentation to rename 'timeout_seconds' to...

Fixed #12195 -- Clarified cache documentation to rename 'timeout_seconds' to 'timeout'. Thanks, galund and timo

git-svn-id: http://code.djangoproject.com/svn/django/trunk@12183 bcc190cf-cafb-0310-a4f2-bffc1f526a37