recv_sideband: Bands #2 and #3 always go to stderr

This removes the last parameter of recv_sideband, by which the callers
told which channel bands #2 and #3 should be written to.

Sayeth Shawn Pearce:

   The definition of the streams in the current sideband protocol
   are rather well defined for the one protocol that uses it,
   fetch-pack/receive-pack:

     stream #1:  pack data
     stream #2:  stderr messages, progress, meant for tty
     stream #3:  abort message, remote is dead, goodbye!

Since both callers of the function passed 2 for the parameter, we hereby
remove it and send bands #2 and #3 to stderr explicitly using fprintf.

This has the nice side-effect that these two streams pass through our
ANSI emulation layer on Windows.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Acked-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-fetch-pack.c

@@ -482,7 +482,7 @@ static int sideband_demux(int fd, void *data)
 {
 	int *xd = data;
 
-	return recv_sideband("fetch-pack", xd[0], fd, 2);
+	return recv_sideband("fetch-pack", xd[0], fd);
 }
 
 static int get_pack(int xd[2], char **pack_lockfile)