Fix-ups for the "continuous random tone" sysop chat pager

I haven't played with this chat pager in *years*! The lowest tones were inaudible (raise the range from 0-800Hz to 400-1200Hz).
Increase the msgabort() tone from 1 to 10ms, sounds like those computerized voice recognition phone systems now.

Remove the redundant "<user> paged you to chat" notifications (and log message) when turning *off* the chat pager.