Split concrete and abstract ctor generation into two separate functions

lib/class_builder.js

@@ -41,7 +41,16 @@ var util           = require( __dirname + '/util' ),
      * Instance id counter, to be incremented on each new instance
      * @type {number}
      */
-    instance_id = 0
+    instance_id = 0,
+
+    /**
+     * Set to TRUE when class is in the process of being extended to ensure that
+     * a constructor can be instantiated (to use as the prototype) without
+     * invoking the class construction logic
+     *
+     * @type {boolean}
+     */
+    extending = false
 ;
 
 
@@ -71,8 +80,6 @@ var enum_bug = (
 exports.ClassBase = function Class() {};
 
 
-exports.build = ( function( extending )
-{
 /**
  * Mimics class inheritance
  *
@@ -85,7 +92,7 @@ exports.build = ( function( extending )
  *
  * @return  {Object}  extended class
  */
-    return function extend()
+exports.build = function extend()
 {
     // ensure we'll be permitted to instantiate abstract classes for the base
     extending = true;
@@ -181,6 +188,29 @@ exports.build = ( function( extending )
 {
     // concrete class
     if ( abstract_methods.__length === 0 )
+    {
+        return createConcreteCtor( cname, members );
+    }
+    // abstract class
+    else
+    {
+        return createAbstractCtor( cname );
+    }
+}
+
+
+/**
+ * Creates the constructor for a new concrete class
+ *
+ * This constructor will call the __constructor method of the class, if
+ * available.
+ *
+ * @param  {string}  cname    class name (may be empty)
+ * @param  {Object}  members  class members
+ *
+ * @return  {function()}  constructor
+ */
+function createConcreteCtor( cname, members )
 {
     var args = null;
 
@@ -247,8 +277,19 @@ exports.build = ( function( extending )
 
     return __self;
 }
-        // abstract class
+
-        else
+
+/**
+ * Creates the constructor for a new abstract class
+ *
+ * Calling this constructor will cause an exception to be thrown, as abstract
+ * classes cannot be instantiated.
+ *
+ * @param  {string}  cname  class name (may be empty)
+ *
+ * @return  {function()}  constructor
+ */
+function createAbstractCtor( cname )
 {
     var __abstract_self = function()
     {
@@ -274,8 +315,6 @@ exports.build = ( function( extending )
 
     return __abstract_self;
 }
-    }
-} )( false );
 
 
 function buildMembers(