[selectors] fix is_instance bug w/ parent classes. Also slight performance enhancements by changing what's returned by vreg['etypes'].parent_classes method (dedicated for this usage...) and removing no more necessary methods

msgid "read_perm"
msgstr ""

msgid "add_perm"
msgstr ""

msgid "update_perm"
msgstr ""

msgid "delete_perm"
msgstr ""