git-am: propagate -C<n>, -p<n> options as well

git-am: propagate -C<n>, -p<n> options as well

These options are meant to deal with patches that do not apply cleanly
due to the differences between the version the patch was based on and
the version "git am" is working on.

Because a series of patches applied in the same "git am" run tends to
come from the same source, it is more useful to propagate these options
after the application stops.

Signed-off-by: Junio C Hamano <gitster@pobox.com>