Usability improvements to the emulab-sync programs:

  * Terminating a TCP client before the barrier is reached will back
    out any changes to the barrier's count.

  * You can SIGHUP the server to clear all of the barriers and release
    the clients with an exit value of 240.

  * Basic error reporting is supported using the "-e" option and the
    program's exit code.

  * On FreeBSD, the server will respond to a SIGINFO (^T) by printing
    out the list of active barriers.

  * More checking of the inputs.