More library functions for worker access

* broker/lib.c (strnlen_s, qisort, ifind, now): new procedures
Modify worker model and data

We're keying off the ZMQ address and the name string, now.

* broker/worker.h (role_t) new type.
  (add_worker) new calling structure
* broker/worker.c: many new worker globals
  (add_worker) new calling structure
  (get_worker) removed for the moment