ACCUMULO-378 Allow for dynamic reconfiguration of the WorkAssigner impl
ACCUMULO-378 Resize the threadpool used for sending data by checking the configuration periodically

Use the SimpleTimer to just schedule a check of the configuration
to see what the value is for the maximum size of the threadpool which
is used with the DistributedWorkQueue and ReplicationProcessor.
ACCUMULO-378 Can't use '_' as the row separator for Order records.

The ULongLexicoder *might* create bytes that actually equal the '_', which
will mess up the splitting logic of the row key. Switch it to a \x00 instead
and find the last instance of it.
ACCUMULO-2847 Add some basic documentation to the user manual for replication