Properly handle error subtype #constructor (#__constructor alias)

Using `#constructor' in place of `#__construct' caused an error attempting
to "redefine" `#__constructor' (once the alias was applied); the system was
making improper assumptions and not accounting for aliases.

In fact, everthing about how this was being done was bad, since adding any
keywords would have thrown it off as well!

* lib/ClassBuilder.js (build): Move ector detection past prop
  parsing.  Check parsed properties instead of raw.
* test/ClassBuilder/ErrorExtendTest.js: Iterate ctor override test on new
    `ctors'.
  (caseSetUp) [ctors]: Add property.

lib/ClassBuilder.js

@@ -447,22 +447,6 @@ exports.prototype.build = function extend( _, __ )
         }
     }
 
-    // we transparently handle extending errors in a sane manner, which is
-    // traditionally a huge mess (you're welcome)
-    if ( this._ector && this._ector.isError( base ) )
-    {
-        // declare public properties (otherwise, they'll be confined to the
-        // private visibility object in ES5+ environments)
-        props.message = '';
-        props.stack   = '';
-
-        // user-provided constructor
-        var ector_own = props.__construct;
-
-        // everything else is handled by the constructor
-        props.__construct = this._ector.createCtor( base, cname, ector_own );
-    }
-
     // increment class identifier
     this._classId++;
 
@@ -508,6 +492,24 @@ exports.prototype.build = function extend( _, __ )
         }
     }
 
+    // we transparently handle extending errors in a sane manner, which is
+    // traditionally a huge mess (you're welcome)
+    if ( this._ector && this._ector.isError( base ) )
+    {
+        // declare public properties (otherwise, they'll be confined to the
+        // private visibility object in ES5+ environments)
+        props.message = '';
+        props.stack   = '';
+
+        // user-provided constructor
+        var ector_own = members[ 'public' ].__construct;
+
+        // everything else is handled by the constructor
+        members[ 'public' ].__construct = this._ector.createCtor(
+            base, cname, ector_own
+        );
+    }
+
     // reference to the parent prototype (for more experienced users)
     prototype.___$$parent$$ = base.prototype;
 

test/ClassBuilder/ErrorExtendTest.js

@@ -38,6 +38,8 @@ require( 'common' ).testCase(
             RangeError,
             URIError,
         ];
+
+        this.ctors = [ '__construct', 'constructor' ];
     },
 
 
@@ -164,7 +166,7 @@ require( 'common' ).testCase(
      * implementation.  However, a user can provide a method to be invoked
      * after the generated constructor.
      */
-    'Can override generated constructor': function()
+    '@each(ctors) Can override generated constructor': function( ctor )
     {
         var called_gen = false,
             called_own = false;
@@ -178,12 +180,13 @@ require( 'common' ).testCase(
             };
         };
 
-        var result = this.builder.build( {}, {
-            __construct: function()
-            {
-                called_own = true;
-            },
-        } )();
+        var dfn = {};
+        dfn[ ctor ] = function()
+        {
+            called_own = true;
+        };
+
+        var result = this.builder.build( {}, dfn )();
 
         this.assertOk( called_gen );
         this.assertOk( called_own );