If some refs could not be read when listing branches, this can now be
observed in the exit status of the "git branch" command.
Signed-off-by: Simo Melenius <simo.melenius@iki.fi> Reviewed-by: Jonathan Nieder <jrnieder@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>