Cleaned up svc_exec using strseg_tok_next

This gets rid of a lot of tricky pointer dancing.
Partial implementation of control.event and control.cmd

Broke controller constructor/cleanup into alloc+ctor+dtor+free
methods.  Added new fields in service to track whether it is
using one of these special handles.  Added state machine state
for allocating the controller and cleaning up if anything fails.

refs #8