Prompt the user to chat with The Guru when sysop is not available

This is actually how sbbs v1/2 worked, before this functionality was moved to
chat_sec.src.

If the sysop doesn't want the prompt at all, just set the string
ChatWithGuruInsteadQ to blank in the ctrl/text.dat file (or copy this script
to mods dir and edit to your liking).

This resolves issue #569.

exec/chat_sec.js

@@ -140,7 +140,8 @@ while(bbs.online && !console.aborted) {
 			bbs.private_chat();
 			break;
 		case 'C':
-			if(!bbs.page_sysop())
+			if(!bbs.page_sysop()
+				&& !deny(format(bbs.text(ChatWithGuruInsteadQ), system.guru || "The Guru")))
 				bbs.page_guru();
 			break;
 		case 'T':