pack-write.c: extract 'write_rev_file_order'
Existing callers provide the reverse index code with an array of 'struct
pack_idx_entry *'s, which is then sorted by pack order (comparing the
offsets of each object within the pack).
Prepare for the multi-pack index to write a .rev file by providing a way
to write the reverse index without an array of pack_idx_entry (which the
MIDX code does not have).
Instead, callers can invoke 'write_rev_index_positions()', which takes
an array of uint32_t's. The ith entry in this array specifies the ith
object's (in index order) position within the pack (in pack order).
Expose this new function for use in a later patch, and rewrite the
existing write_rev_file() in terms of this new function.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>