* The linktest daemon (the one that runs on the nodes) no longer talks
  to boss directly, but instead contacts the local elvind; rc.linktest
  is changed to reflect that.

* A bunch of signal handler changes to run_linktest.pl; do not rely on
  events to stop linktest when it is running on boss; when the user
  kills a running linktest make sure all the processes are killed
  explicitly.

* New wrapper script (linktest_control) for use on boss, specifically
  when being called from the web interface. This script handles the DB
  part (getting linktest_level and linktest_pid), making sure that
  only one linktest is running at a time (on boss) and reseting the
  pid in the DB as needed. The -k option kills a running linktest, and
  is invoked from the web interface when the user wants to kill one in
  progress. This gets the pid from the DB and sends it a TERM signal,
  which sends a TERM to the run_linktest.pl script, which sends a TERM
  to the ltevent helper app.

  Note that this wrapper is also suitable for the XMLRPC interface,
  although I have not added it there yet.