Replace git multi-pack-index expire/repack with upstream v6

Documentation/git-multi-pack-index.txt

@@ -37,15 +37,21 @@ expire::
 	afterward to remove all references to these pack-files.
 
 repack::
-	Collect a batch of pack-files whose size are all at most the
-	size given by --batch-size, but whose sizes sum to larger
-	than --batch-size. The batch is selected by greedily adding
-	small pack-files starting with the oldest pack-files that fit
-	the size. Create a new pack-file containing the objects the
-	multi-pack-index indexes into those pack-files, and rewrite
-	the multi-pack-index to contain that pack-file. A later run
-	of 'git multi-pack-index expire' will delete the pack-files
-	that were part of this batch.
+	Create a new pack-file containing objects in small pack-files
+	referenced by the multi-pack-index. If the size given by the
+	`--batch-size=<size>` argument is zero, then create a pack
+	containing all objects referenced by the multi-pack-index. For
+	a non-zero batch size, Select the pack-files by examining packs
+	from oldest-to-newest, computing the "expected size" by counting
+	the number of objects in the pack referenced by the
+	multi-pack-index, then divide by the total number of objects in
+	the pack and multiply by the pack size. We select packs with
+	expected size below the batch size until the set of packs have
+	total expected size at least the batch size. If the total size
+	does not reach the batch size, then do nothing. If a new pack-
+	file is created, rewrite the multi-pack-index to reference the
+	new pack-file. A later run of 'git multi-pack-index expire' will
+	delete the pack-files that were part of this batch.
 
 
 EXAMPLES

builtin/multi-pack-index.c

@@ -49,7 +49,7 @@ int cmd_multi_pack_index(int argc, const char **argv,
 	if (!strcmp(argv[0], "repack"))
 		return midx_repack(the_repository, opts.object_dir, (size_t)opts.batch_size);
 	if (opts.batch_size)
-		die(_("--batch-size option is only for 'repack' verb"));
+		die(_("--batch-size option is only for 'repack' subcommand"));
 
 	if (!strcmp(argv[0], "write"))
 		return write_midx_file(opts.object_dir);
@@ -58,5 +58,5 @@ int cmd_multi_pack_index(int argc, const char **argv,
 	if (!strcmp(argv[0], "expire"))
 		return expire_midx_packs(the_repository, opts.object_dir);
 
-	die(_("unrecognized verb: %s"), argv[0]);
+	die(_("unrecognized subcommand: %s"), argv[0]);
 }