Monitoring of single tasks in work queue.

If the queue is created with the function
work_queue_create_monitoring (instead of just work_queue_create),
every task submitted is wrapped in the resource_monitor, and a
summary of the resources used is returned. Right now every task
generated a summary file, but this will we consolidated to a
single file in the near future.
There can be only one (work queue resouce summary)

All resource summaries are appended to a single summary file per
work_queue_task.
Adds record locking to work queue resource summary

If the file specified for the summary already exist, then the
individual summaries are appended to it. A queue has to request
the lock of the file, which makes possible for several queues to
share the same resource summary file.