get_patch_ids() takes an already initialized rev_info and a
prefix. The prefix is used when initalizing a second rev_info. Since
the initialized rev_info already has a prefix and the prefix never
changes, we can use the prefix from the initialized rev_info to
initialize the second rev_info.
Signed-off-by: Martin von Zweigbergk <martin.von.zweigbergk@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>