git-pull.sh: better warning message for "git pull" on detached head. Otherwise, git complains about not finding a branch to pull from in 'branch..merge', which is hardly understandable. While we're there, reword the sentences slightly. Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr> Signed-off-by: Junio C Hamano <gitster@pobox.com>