clarify: does "Dog is Mammal" load Mammal for you?

[Mark Stosberg]

In S12, we see a number examples of:

  class Dog is Mammal
  http://dev.perl.org/perl6/doc/design/syn/S12.html
However, it's not clear if it is necessary to preload Mammal for Dog
to function properly here, or what that syntax would be.

Testing with current version of pugs, this doesn't happen. Adding
"use Mammal" before this syntax seems to fix it, but doesn't seem like
it should be necessary, especially since "use Mammal" has traditionally 
implied as "has-a" relationship.

   Mark