changed managerss.php such that:
- one can subscribe to the rssfeed of any user by using the global rss credentials
  (this is fine for admins, but i dont like the idea, that a normal user can read anyones content if they have the global rss credentials)
- users can subscribe to their own content by using their user credentials
  (in this the id assigned to the user is used instead of the id passed by the get parameter)
my auth mechanism implemented before did not work, if no global rss-user
settings were present. so, i restrctured the order of checks and now it
should work.
Merge branch 'userform-correction' into global-and-user-rss-auth
Merge branch 'global-and-user-rss-auth' into SRSoftware-Mix