[reSIProcate] Redirect API

[Derek MacDonald]

RedirectManager has been added to DUM. Applications control whether a target
will be attempted by implemented RedirectHandler::onTryingNextTarget

There has been a change to InviteSessionHandler:

  virtual void onRedirected(ClientInviteSessionHandle, const SipMessage&
msg)=0;

which is like an onTermintated, except the DialogSet will not be destroyed
if this was the last Dialog.    This is called in the case where a 18x
establishes then a 3xx is received.

3xxs may still be dispatched to onTerminated: 380, 305 and any 3xx which
does not have any acceptable targets. A 3xx received in a Dialog(not an
early dialog) will be ignored. 

Derek