Column doesn't need to use delayed runtime valueExpressionMixin

lib/column.js

@@ -7,7 +7,6 @@ var OrderByColumnNode = require(__dirname + '/node/orderByColumn');
 var UnaryNode = require(__dirname + '/node/unary');
 var TextNode = require(__dirname + '/node/text');
 
-var valueExpressionMixed = false;
 var Column = function(config) {
   this.table = config.table;
   for(var name in config) {
@@ -20,15 +19,11 @@ var Column = function(config) {
     direction: new TextNode('DESC')
   });
   this.dataType = config.dataType;
-  // Delay mixin to runtime, when all nodes have been defined, and
-  // mixin only once.  This is to avoid circular dependency in
-  // CommonJS.
-  if (!valueExpressionMixed) {
-    valueExpressionMixed = true;
-    _.extend(Column.prototype, valueExpressionMixin());
-  }
 };
 
+// mix in value expression
+_.extend(Column.prototype, valueExpressionMixin());
+
 var contextify = function(base) {
   var context = Object.create(Column.prototype);
   Object.keys(base).forEach(function (key) {