shallow: migrate shallow information into the object parser

We need to convert the shallow functions all at the same time
as we move the data structures they operate on into the repository.

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

object.h

@@ -16,6 +16,10 @@ struct parsed_object_pool {
 	/* parent substitutions from .git/info/grafts and .git/shallow */
 	struct commit_graft **grafts;
 	int grafts_alloc, grafts_nr;
+
+	int is_shallow;
+	struct stat_validity *shallow_stat;
+	char *alternate_shallow_file;
 };
 
 struct parsed_object_pool *parsed_object_pool_new(void);