* Implement an extensible Block::prevents( <action> ) function to replace the plethor...

* Implement an extensible Block::prevents( <action> ) function to replace the plethora of direct member variable accesses  This pushes the historic *disable*-createaccount-vs-*allow* usertalk-edit wierdness down to the database layer
* Implement accessors for isHardblock() and getRangeStart()/getRangeEnd() in the same fashion.
* Make the corresponding variables private, removing external accessors.  This required updating AbuseFilter with non-B/C code, so I also implemented the rest of the changes I've made to the blocking backend in that extension.
* Move the "get an IP range which encompasses the given IP/range" logic to Block.php; will be needed later... :D