Need to fail split if SPLIT znode is deleted even before the split is completed.

This came up after the following mail in dev list
'infinite loop of RS_ZK_REGION_SPLIT on .94.2'.
The following is the reason for the problem
The following steps happen
-> Initially the parent region P1 starts splitting.
-> The split is going on normally.
-> Another split starts at the same time for the same region P1. (Not sure why this started).
-> Rollback happens seeing an already existing node.
-> This node gets deleted in rollback and nodeDeleted Event starts.
-> In nodeDeleted event the RIT for the region P1 gets deleted.
-> Because of this there is no region in RIT.
-> Now the first split gets over. Here the problem is we try to transit the node to SPLITTING to SPLIT. But the node even does not exist.
But we don take any action on this. We think it is successful.
-> Because of this SplitRegionHandler never gets invoked.