Fixed #7616 -- Added advice on unix socket permissions and umasks to fastcgi...

Fixed #7616 -- Added advice on unix socket permissions and umasks to fastcgi deployment documentation. Thanks to Malcolm Tredinnick for the report and advice, and PaulM and cramm for reviewing the patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14276 bcc190cf-cafb-0310-a4f2-bffc1f526a37