There are at least two cases where we can avoid some mutex locks in ClusterCursorManager class:

• ClusterCursorStats::appendAtLeaf() calls ClusterCursorManager::stats() and ClusterCursorManager::cursorsTimedOut(), both of which require a mutex lock. For both methods appendAtLeaf() is the only caller, so we can combine them.

• ClusterCursorManager::killMortalCursorsInactiveSince locks two times, which also can be reduced to just one lock.