o remove interconnect_env() and place functionality into interconnect_attach()

 o session manager waits for processes in its session, not just children.
   This fixes a problem when tasks are being attached to by a debugger.
 o Add elanhosts.[ch] for Elan host config file parsing. Used in slurm
   to install ElanID/hostname pairs into the kernel. Note that the format
   of the elanhosts config file has changed.