Add getIsPatient accessor to 1.10.x, 1.11.x, and 1.12.x lines

Starting in OpenMRS 2.0.x, we deprecated the isPatient method on Person in favor of getIsPerson (see TRUNK-2205).

We don't want to backport this full change to the 1.x line, because it's too significant, but we do want to add the getIsPatient method to the line so that the isPatient property can be accessed via REST.