SgEntitySchemaInfo now store unsupported field infos.

Before Entity schema infos would throw away unsupported fields, now
they will store them as unsupported field infos.  Unsupported field
infos can be accessed by calling fieldInfosUnsupported().  Unsupported
fields are still not added to Entity objects.

When a field warned that it was of unsupported return type you had to
pull the schema down to figure out why.  Now that they are kept alive
as part of the Entity schema info they can be accessed quicker for
inspection.