added a Load metric to the DHashDescription. created a TimeLock that measures the fraction of time it is write locked
using a common.TimeLock instead of sync.RWMutex in Tree, allowing Tree to tell us about its load.
added the Load metric to the returned DHashDescription
made the dhash/json_server send a new RingChange every second to ensure an updated client
added the load metric
made all RingChange events trigger updates of the internal state and interface
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