Adds override funcionality to permit people to be added to allocations even
if not otherwise permitted by policy, or banned from allocations that they
would otherwise be in per policy.

Also includes additional cleanup:

  * Usernames in the output are now separated by commas since this is
    the format required by the CAEN HPC Group allocation userlist management
    scripts.

  * All error messages are now sent to stdout rather than a mixture of
    stderr and stdout, in order to ensure that when using the --debug option
    that the error messages are next to the debugging output that they
    pertain to.  (The C library output buffering was causing problems with
    this).