Added -E option to work_queue_pool to allow adding extra worker options (in addition to the already supported -t -C -N -o options) to the workers managed by the pool.

For example, if you run the following:
    work_queue_pool -a -N myproj -E '-b 120 -o mydebug')

The '-b 1200 -o mydebug' options would be added to every worker started by this pool.