that clients and servers can avoid using hardwired ports on those
experimental nodes. I have added the following tmcd operation:

	tmcc portregister <service> [<port>]

where we assume its the control network IP (from the DB), and the pid/eid
of the node the experiment belongs to. The given port is entered into
the port_registration table for the experiment, using the service as the
tag. Supplying port=0 clears the registration from the table.

When called like:

	tmcc portregister <service>

we return the registered port, or nothing.

I hacked up a little C library module in libtb so that there is something
that looks like a C interface to this:

 	int
 	PortRegister(char *service, int port);

 	int
 	PortLookup(char *service, char *hostname, int namelen, int *port);

The above routines call out to tmcc of course.

Lastly, I changed the sync server and client to use the new port
registration, via the library calls above.

There are other emulab services that need to be changed as well, but
they can be done on an as needed basis.