'Add a list of transitions to the start of the transition list.
Parameters:
- `names`: a list of transition names.
- `transitions`: a mapping of names to transition tuples.
Exceptions: `DuplicateTransitionError`, `UnknownTransitionError`.'

def add_transitions(self, names, transitions):

    for name in names:
        if self.transitions.has_key(name):
            raise DuplicateTransitionError(name)
        if (not transitions.has_key(name)):
            raise UnknownTransitionError(name)
    self.transition_order[:0] = names
    self.transitions.update(transitions)
