Pass -oControlMaster=no

Otherwise, some options (I noticed particularly ForwardAgent=no) will
get applied across all future sessions on that control socket if the
user has configured ControlMaster=auto for that host and we happen to be
the session to start the socket.

I'm not 100% sure if I picked the right place to put this; maybe it
belongs after ForwardAgent=no is appended later.

scp.c

@@ -505,6 +505,7 @@ main(int argc, char **argv)
 	addargs(&args, "-oClearAllForwardings=yes");
 	addargs(&args, "-oRemoteCommand=none");
 	addargs(&args, "-oRequestTTY=no");
+	addargs(&args, "-oControlMaster=no");
 
 	fflag = Tflag = tflag = 0;
 	while ((ch = getopt(argc, argv,