Added method get_all_alternative_translations():

  Args       : None
  Example    :

    my @alt_translations =
      @{ $transcript->get_all_alternative_translations() };

  Description:  Fetches all alternative translations defined for this
                transcript.  The canonical translation is not returned.

  Returntype : Array reference to Bio::EnsEMBL::Translation
  Exceptions : None
  Caller     : General
  Status     : Stable


Added method add_alternative_translation():

  Args       : Bio::EnsEMBL::Translation $translation
  Example    :

    $transcript->add_alternative_translation($translation);

  Description: Adds an alternative translation to this transcript.
  Returntype : None
  Exceptions : None
  Caller     : General
  Status     : Stable