updated Gearman/Client to consistently choose a job server

for a set function workload and a same ordered list of
job servers all Clients will select the same job server
for that task. This will guaranty the best coelessing
of work possible.
Job server selection based on unique parameter rather than job workload

The workload may contain data that should not be used in determining
uniqueness of a job.  Select the job server based on the unique
parameter instead.