use find_attribute_by_name instead of get_attribute

this is because the former does tree traversal, but the latter does not.

Thus, without this change, anything that does dumpconfig will barf as
soon as it is extended.
v0.003001

 [Bugfix]
 - use instance->meta->find_attribute_by_name().
 - because: PACKAGE-> can't be used because roles don't work
 - because: dumpconfig( __PACKAGE__ , attrs ... ) assumes that the instance will have the attr
 - because: $instance->get_attribute() doesn't trace inheritance.
post-release cleanup