Add table for completed tasks to be sent back to the master.

The table marks which tasks are ready to be sent to the master. A task
is cleared from the table on the kill message from the master.
Send a single available_results message.
worker sends completed tasks on "send_results n".

Where n is the maximum number of results to send back. n == -1 means
send all.
process_*result? did not use stoptime as a parameter.
Wait for result messages when receiving 'available_results'.
Foreman sends completed tasks on "send_results n"
Keep a list of workers with available results.
Print foreman's debug messages every 10 seconds.