Fix @-code replacment logic in newuser.msg

Fix 2 issues with commit 680e30d8:
1. Need to replace @-code globally, otherwise only the first @-code was replaced
2. Need to strip the leading and trailing @'s from the code before passing to bbs.atcode() - fix for issue #527

exec/newuser.js

@@ -142,7 +142,7 @@ function send_newuser_welcome_msg(fname)
 		subject: "Welcome to " + system.name + "!" 
 	};
 
-	msgtxt = msgtxt.replace(/@(\w+)@/, function (code) { return bbs.atcode(code); });
+	msgtxt = msgtxt.replace(/@(\w+)@/g, function (code) { return bbs.atcode(code.slice(1, -1)); });
 	var result = msgbase.save_msg(hdr, msgtxt);
 	if(!result)
 		log(LOG_ERR, "!ERROR " + msgbase.error + " saving mail message");