Bug fixes to make JS/Agent and Voxel Editing work better

- bug fixes to JurisdictionListener - make sure it doesn't flood the servers with JURISDICTION_REQUESTs
- bug fixes to PacketSender - handle the minimal packet sending case better in threaded mode by sleeping at least once per process
- addition of packetsToSendCount() method to Voxels JS interface to allow scripts to know if they are generating too many packets and or have extra packets still to send