minor: elaborate method doc on Scene.NewUserConnection()
Lock on AgentCircuitData during Scene.AddClient() and RemoveClient() to prevent an inactive connection being left behind if the user closes the viewer whilst the connection is being established.

This should remove the need to run the console command "kick user --force" when these connections are left around.
minor: Add method doc to EventManager.OnNewClient, OnClientLogin, ClientClosed, OnRemovePresence that any long-running operations should be launched on a thread separate to the event thread.
Remove osDropAttachment threat level check wrongly placed in OSSL_Api.ShoutErrorOnLackingOwnerPerms.
Correct osSetContentType() threat check to query osSetContentType rather than osSetResponseType
Add "delete object pos <start-coord> to <end-coord>" console command.

This allows one to delete objects within a certain volume.
See help on console for more details.
Assign endVector before control leaves ObjectCommandsModule.TryParseVectorRange() in order to fix mono 2.4.3 compile failure.

This doesn't fail the compile on mono 2.10.8.
Updated Robust.HG.ini.example. Thanks Austin Tate.
BulletSim: Fix crash when linking large physical linksets.
Properly remove and restore linkage constraints when upgrading
    a prim's mesh to a hull.
Lots more debug logging.
Definitions and use of Bullet structure dumping.
Centralize detail logging so a Flush() can be added for debugging.
BulletSim: Add Force* operations to objects to allow direct push to engine.
Update BSDynamics to use same (don't want to delay updates til next taint-time.
Suppress queuing a taint update for position and orientation calls if value
    does not change.
Move Bullet timing statistics call from C# back to C++ code.
Throttle taints per simulation step and add parameter to set.
By default, don't create hulls for physical objects. Add a
    parameter to turn on and off.
BulletSim: cosmetic changes (comments and renaming). Give mass to terrain to improve interactions.
BulletSim: Change defaults for constraint CFM and ERP to make large linksets more rigid. Remove mass calculation for terrain (it should stay a static object).
BulletSim: Use full linkset mass when computing vehicle gravity force. Add taint-time specification to new AddForce().
BulletSim: normalize physics FPS to 45.
BulletSim: normalize physics FPS to 45 (for real this time).
BulletSim: remove some unused API2 calls because they were removed from Bullet 2.81
BulletSim: update the DLLs and SOs
Extend "show stats" command to "show stats [list|all|<category name>]"

This allows different categories of stats to be shown, with options to list categories or show all stats.
Currently categories are scene and simulator and only a very few stats are currently registered via this mechanism.
This commit also adds percentage stats for packets and blocks reused from the packet pool.
Merge branch 'master' of ssh://opensimulator.org/var/git/opensim
Fix packetpool for ImprovedTerseObjectUpdate packets.

These were neither being returned or in many places reused.
Getting packets from a pool rather than deallocating and reallocating reduces memory churn which in turn reduces garbage collection time and frequency.