The "Pushing submodule <foo>" progress output correctly goes to
stderr, but "Fetching submodule <foo>" is going to stdout by
mistake. Fix it to write to stderr.
Noticed while trying to implement a parallel submodule fetch. When
this particular output line went to a different file descriptor, it
was buffered separately, resulting in wrongly interleaved output if
we copied it to the terminal naively.
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com> Signed-off-by: Stefan Beller <sbeller@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>