Fixing c2mop:direct-slot-definition-class methods to return a class (#187)

Right now they return symbols, which is not the correct return type
based on the AMOP Book Specification which is the official
specification adopted by the ANSI Spec.

See
https://lisp-docs.github.io/cl-language-reference/meta-object-protocol/dictionary/direct-slot-definition-class

and

https://lisp-docs.github.io/cl-language-reference/meta-object-protocol/dictionary/effective-slot-definition-class

Or http://metamodular.com/CLOS-MOP/direct-slot-definition-class.html

and

http://metamodular.com/CLOS-MOP/effective-slot-definition-class.html

Author: daninus14

src/core/class/table.lisp

@@ -141,7 +141,7 @@
       class)))
 
 (defmethod c2mop:direct-slot-definition-class ((class table-class) &key &allow-other-keys)
-  'table-column-class)
+  (find-class 'table-column-class))
 
 (defmethod c2mop:effective-slot-definition-class ((class table-class) &rest initargs)
   (declare (ignorable initargs))

src/core/dao/mixin.lisp

@@ -76,7 +76,7 @@
 (defclass dao-table-mixin (table-class) ())
 
 (defmethod c2mop:direct-slot-definition-class ((class dao-table-mixin) &key)
-  'dao-table-column-class)
+  (find-class 'dao-table-column-class))
 
 (defmethod c2mop:effective-slot-definition-class ((class dao-table-mixin) &rest initargs)
   (declare (ignorable initargs))

src/core/dao/table.lisp

@@ -39,7 +39,7 @@
                       :initform '(t))))
 
 (defmethod c2mop:direct-slot-definition-class ((class dao-table-class) &key)
-  'dao-table-column-class)
+  (find-class 'dao-table-column-class))
 
 (defmethod c2mop:effective-slot-definition-class ((class dao-table-class) &rest initargs)
   (declare (ignorable initargs))

src/core/dao/view.lisp

@@ -19,7 +19,7 @@
        :reader dao-table-view-as-query)))
 
 (defmethod c2mop:direct-slot-definition-class ((class dao-table-view) &key)
-  'dao-table-column-class)
+  (find-class 'dao-table-column-class))
 
 (defmethod c2mop:effective-slot-definition-class ((class dao-table-view) &rest initargs)
   (declare (ignorable initargs))