use of the recursive inheritance while resolving a method or doing a
C<$foo-E<gt>isa($bar)> lookup.
-=head2 warnings::register changed to favor users of modules
+=head2 warnings::enabled and warnings::warnif changed to favor users of modules
The behaviour in 5.10.x favors the person using the module;
The behaviour in 5.8.x favors the module writer;