OUT/Ephemeral: complete transformation refactoring

This removes the special semantics we had for the become method which
was just overkill.  Instead of forcing vetoing of ephemeral
transformations into the ephemerals themselves, we now allow a call-back
based "Adjudication" process which allows interested parties to
register for veto power of an ephemeral's transformation via a separate
mix-in class which is not itself required to be ephemeral.

Signed-off-by: Gregory M. Turner <gmt@be-evil.net>