[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

option_group_changed('port', 'main', 'web')
option_group_changed('query-log-file', 'main', 'web')
option_group_changed('profile', 'main', 'web')
option_group_changed('max-post-length', 'main', 'web')