git: update to v2.10.0

Upstream continues to replace unsigned char *sha1 with struct
object_id old_oid. This makes the required changes.

The git lib has its own main function now. Rename our main function
to cmd_main, it is called from main then.

ui-log.c

@@ -49,7 +49,7 @@ static void inspect_files(struct diff_filepair *pair)
 
 	files++;
 	if (ctx.repo->enable_log_linecount)
-		cgit_diff_files(pair->one->sha1, pair->two->sha1, &old_size,
+		cgit_diff_files(&pair->one->oid, &pair->two->oid, &old_size,
 				&new_size, &binary, 0, ctx.qry.ignorews,
 				count_lines);
 }