git: update to v2.16.0

Update to git version v2.16.0:

* refs: convert resolve_ref_unsafe to struct object_id
  (49e61479be913f67e66bb3fdf8de9475c41b58bd)
* diff: remove DIFF_OPT_SET macro
  (23dcf77f48feb49c54bad09210f093a799816334)
* log: add option to choose which refs to decorate
  (65516f586b69307f977cd67cc45513a296cabc25)
* diff: convert flags to be stored in bitfields
  (02f2f56bc377c287c411947d0e1482aac888f8db)

Signed-off-by: Christian Hesse <mail@eworm.de>

shared.c

@@ -346,7 +346,7 @@ void cgit_diff_tree(const struct object_id *old_oid,
 	opt.output_format = DIFF_FORMAT_CALLBACK;
 	opt.detect_rename = 1;
 	opt.rename_limit = ctx.cfg.renamelimit;
-	DIFF_OPT_SET(&opt, RECURSIVE);
+	opt.flags.recursive = 1;
 	if (ignorews)
 		DIFF_XDL_SET(&opt, IGNORE_WHITESPACE);
 	opt.format_callback = cgit_diff_tree_cb;