The reactor code is currently being re-implemented using zeromq.  All zeromq
work needs to be isolated from as much of CASTOR as possible.  For the time
being this means the reactor code should stay within the scope of tape
developements where zeromq is being investigated.

Added check with VMGR that migration requests coming from the gateway imply a BUSY status of the tape in VMGR

This commit also moves derived classes.

This commit can be considered another step towards removing the need for
a separate tape directory.

As a step closer to removing the need for a separate castor/tape
directory, I have moved castor::tape::legacymsg to
castor::legacymsg.

PollReactorImpl objects own their handlers and therefore need to delete
them where appropriate.  A handler knows when it should be removed from
its reactor and deleted from the heap.  The
PollEventHandler::handleEvent() method a handler now returns true if the
handler wants its reactor to remove and delete it.

Fixed h/rfcntl.h which missed multiple inclusion guards entirely.

This commit adds code to the tapeserverd daemon to register its
drives with the vdqmd daemon.  There is a problem with the code
in that it fails to register two drives in the up state.  This
will be fixed later.