Replaced __define[GS]etter__ with defineProperty for prop proxy

lib/propobj.js

@@ -90,18 +90,23 @@ exports.createPropProxy = function( base, dest, props )
 
         ( function( prop )
         {
+            // just in case it's already defined, so we don't throw an error
+            dest[ prop ] = undefined;
+
             // public properties, when set internally, must forward to the
             // actual variable
-            dest.__defineSetter__( prop, function( val )
+            Object.defineProperty( dest, prop, {
+                set: function( val )
                 {
                     base[ prop ] = val;
-            } );
+                },
 
-            // since we're defining a setter, we'll need to define a getter
-            // to return the value, or we'll simply return undefined
-            dest.__defineGetter__( prop, function()
+                get: function()
                 {
                     return base[ prop ];
+                },
+
+                enumerable:   true,
             } );
         } ).call( null, prop );
     }