- [bug] Fixed bug mostly local to new

- [bug] Fixed bug mostly local to new
AbstractConcreteBase helper where the "type"
attribute from the superclass would not
be overridden on the subclass to produce the
"reserved for base" error message, instead placing
a do-nothing attribute there.  This was inconsistent
vs. using ConcreteBase as well as all the behavior
of classical concrete mappings, where the "type"
column from the polymorphic base would be explicitly
disabled on subclasses, unless overridden
explicitly.