Extended "client-kill" management interface command (server-side)

Extended "client-kill" management interface command (server-side)
to accept an optional message string.  The message string format is:

  RESTART|HALT,<human-readable-message>

RESTART will tell the client to restart (i.e. SIGUSR1).

HALT will tell the client to exit (i.e. SIGTERM).

On the client, human-readable-message will be communicated via
management interface:

  >NOTIFY,<severity>,<type>,<human-readable-message>"

Version 2.1.3m

git-svn-id: http://svn.openvpn.net/projects/openvpn/branches/BETA21/openvpn@7063 e7ae566f-a301-0410-adde-c780ea21d3b5