* sql/metaclass.lisp: Work-around openmcl's CHANGE-CLASS
changing the type-specifier. Use a lisp type of (OR NULL FOO)
for a specified-type of FOO unless :db-constraints :not-null.
+ No need to specialize finalize-inheritance for openmcl.
* tests/test-*.lisp: Rename fields so that joins occur on
fields with different names. This ensures that join code is
selecting the proper name.