object.c: skip prepending modules

* object.c (rb_obj_is_kind_of): skip prepending modules.
  [ruby-core:54742] [Bug #8357]
* object.c (rb_class_inherited_p): ditto.
  [ruby-core:54736] [Bug #8357]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40561 b2dd03c8-39d4-4d8f-98ff-823fe69b080e