Add scoped finders to relations

[dhumphreys]

Should allow standard finding methods, or at least findByKey on relation objects. This should allow for scoped finding, such as rel.where("createdAt > ?", ["2011-06-01"]).findByKey(433). This method would return a model object, not a relation. This should allow for scoping at the model level. Dynamic finders may be possible at some point.

CFWheels example:

<cfscript>
  // assuming findAll returned as a relation
  model("order").findAll(where="status='complete'").findByKey(424);

  // or using a relation
  model("order").where(status="complete").findByKey(424);

  // or with some sort of named scope plugin
  model("order").completed().findByKey(424);

  // assuming association is returned as a relation
  model("user").orders().findByKey(435);
</cfscript>