Change logging to provide more information on LLUDPServer.HandleCompleteMovementIntoRegion()

Add more information on which endpoint sent the packet when we have to wait and if we end up dropping the packet
Only check if the client is active - other checks are redundant since they can only failed if IsActve = false
Double the time spent waiting for a UseCircuitCode packet in LLUDPServer.HandleCompleteMovementIntoRegion()

This is to deal with one aspect of http://opensimulator.org/mantis/view.php?id=6755
With the V2 teleport arrangements, viewers appear to send the single UseCircuitCode and CompleteAgentMovement packets immediately after each other
Possibly, on occasion a poor network might drop the initial UseCircuitCode packet and by the time it retries, the CompleteAgementMovement has timed out and the teleport fails.
There's no apparant harm in doubling the wait time (most times only one wait will be performed) so trying this.
minor: Make log message when Scene.IncomingChildAgentDateUpdate() more explicit that there is a problem if it still finds the agent to be a child if the sender wanted to wait till it became root

Add some comments about the mssage sequence, though much more data is at
http://opensimulator.org/wiki/Teleports
refactor: rename *ChildAgentDataUpdate() methods to *UpdateChildAgent()

verb-noun is consistent with other similar methods
minor: correct method name in comment