REGISTRAR: check for similar users when auto-approving application

- If VO's initial application is set to auto-approve mode, then stop
  the process, when similar users are found and notify VO admin
  about the problem. Application can be then approved manually.

- Other types of application doesn't create new User, so we don't have
  to check for similar users.
Merge pull request #431 from zlamalp/nonapprove

REGISTRAR: check for similar users when auto-approving application