Support expressions in dao properties

[TomK]

This code would correctly update priority on an unloaded row; based on urgency, impact and type.

$ticket = new Ticket();
$ticket->id = 123;
$ticket->priority = AdditionExpression::create(
  'urgency',
  'impact',
  IfExpression::create(
    EqualPredicate::create('type','question'),
    10,
    0
  )
); 
$ticket->save();