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>

ui-diff.c

@@ -444,7 +444,7 @@ void cgit_print_diff(const char *new_rev, const char *old_rev,
 
 		diff_setup(&diffopt);
 		diffopt.output_format = DIFF_FORMAT_PATCH;
-		DIFF_OPT_SET(&diffopt, RECURSIVE);
+		diffopt.flags.recursive = 1;
 		diff_setup_done(&diffopt);
 
 		ctx.page.mimetype = "text/plain";