builtin/pack-redundant: avoid casting buffers to struct object_id

builtin/pack-redundant: avoid casting buffers to struct object_id

Now that we need our instances of struct object_id to be zero padded, we
can no longer cast unsigned char buffers to be pointers to struct
object_id.  This file reads data out of the pack objects and then
inserts it directly into a linked list item which is a pointer to struct
object_id.  Instead, let's have the linked list item hold its own struct
object_id and copy the data into it.

In addition, since these are not really pointers to struct object_id,
stop passing them around as such, and call them what they really are:
pointers to unsigned char.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>