- [bug] Fixed bug whereby a subclass of a subclass

- [bug] Fixed bug whereby a subclass of a subclass
using concrete inheritance in conjunction with
the new ConcreteBase or AbstractConcreteBase
would fail to apply the subclasses deeper than
one level to the "polymorphic loader" of each
base  [ticket:2312]

- [bug] Fixed bug whereby a subclass of a subclass
using the new AbstractConcreteBase would fail
to acquire the correct "base_mapper" attribute
when the "base" mapper was generated, thereby
causing failures later on.  [ticket:2312]