This doesn't seem to fix any leaks, but I'm pretty sure it's the right thing
to do, since we weaken this slot when creating a new method.
my $self = shift;
my $clone = bless { %{$self}, @_ }, blessed($self);
+ weaken($clone->{associated_metaclass}) if $clone->{associated_metaclass};
$clone->_set_original_method($self);