Fixes race condition on jobs being done before handler is set.

When receiving a response, what was happening

1. Read bufferSize and it gets assigned to leftdata
2. Read another bufferSize
3. 2 buffers get appended, but leftdata still points to first buffer
4. Process data buffer which contains only complete responses
5. Back to ReadLoop, but leftdata still points to first incomplete buffer
    causing corrupt data to be processed

Solution is to make leftdata nil once we have merged it with the second buffer

--HG--
branch : 0.1
rename : worker/jobagent.go => worker/agent.go
rename : worker/workerjob.go => worker/job.go

--HG--
branch : 0.1

--HG--
branch : 0.1
rename : gearman/client/client.go => client/client.go
rename : gearman/client/client_test.go => client/client_test.go
rename : gearman/client/clientjob.go => client/job.go
rename : gearman/gearman.go => common/gearman.go
rename : gearman/worker/jobagent.go => worker/jobagent.go
rename : gearman/worker/worker.go => worker/worker.go
rename : gearman/worker/worker_test.go => worker/worker_test.go
rename : gearman/worker/workerjob.go => worker/workerjob.go