* Allow blocks on anonymous users only.

* Allow blocks on anonymous users only.
* Allow or disallow account creation from blocked IP addressess on a per-block basis.
* Prevent duplicate blocks.
* Fixed the problem of expiry and unblocking erroneously affecting multiple blocks.
* Fixed confusing lack of error message when a blocked user attempts to create an account.
* Fixed inefficiency of Special:Ipblocklist in the presence of large numbers of blocks; added indexes and implemented an indexed pager.