Allow a node type's property definition to override a supertype's, as long as constraints are more restrictive

A node type N' should be able to define a property definition D' that overrides a corresponding property definition D in a supertype N, as long as D' is as- or more-constrained than D.

Currently, if D' and/or D define constraints, then ModeShape expects both definitions to have constraints that match exactly. IOW, it is not possible to override a definition with a definition that is more constrained.