- JS system.operator_available property (read/writeable)
- SYSAVAIL @-code which expands to LiSysopAvailable or LiSysopNotAvailable
  (use the new SYSAVAIL @-code in the chat menu to show availabilty to chat)
- ;avail sysop command (in str_cmds.js) to toggle sysop availability
- Changed LiSysopIs text.dat string to be a format string (include %s) and
  the trailing \r\n, so that it can be used in str_cmds.js or anywhere else
  to report sysop availability to chat, or can be set to blank string to
  display nothing (this would not work previously).