In Git v2.0, we will change the default --prefix for init/clone from
none/empty to "origin/" (which causes SVN-tracking branches to be
placed at refs/remotes/origin/* instead of refs/remotes/*).
This patch warns users about the upcoming change, both in the git-svn
manual page, and on stderr when running init/clone in the "multi-mode"
without providing a --prefix.
Cc: Eric Wong <normalperson@yhbt.net> Signed-off-by: Johan Herland <johan@herland.net> Signed-off-by: Eric Wong <normalperson@yhbt.net>