Cycle through all available jobs until match found.

Previously, only the first job in the queue was scanned to see if a
worker was available.  This means that jobs were only executed on a
strict first-come-first-served basis.  Now all queued jobs are
checked each cycle, and when the first match is found that job is
run and the rest of the network cycle continues.
Changed reply of SERVER-JOBS meta information.

The existing ZMQ message object was used to reply to system meta
requests.  This left any calling parameters on the object and
confused the reply.  A fresh ZMQ message object is created when
replying to SERVER-JOBS.  This helps with JSONP functionality.