This new operators allows a PDO-like binding, specifying a clause and a
binding type. For instance:
$c->add('foo = ?', 123, Criteria::RAW, PDO::PARAM_STR);
This is especially necessary for `having()` clauses, because the
conditions are often based on calculated columns, for which Propel
cannot guess the binding type.
This shouls keep the Criteria API to a fairly limited number of methods, although it now behaves a little more magically than before. But doing things the proper way requires a more important refactoring, which can happen in Propel2 but not anymore in the 1.x branch