Use a more robust check for whether a variable is a date

The simple "instanceof Date" check fails if the Date was made in a
different node.js VM

boot/boot.js

@@ -76,6 +76,13 @@ $tw.utils.isArray = function(value) {
 	return Object.prototype.toString.call(value) == "[object Array]";
 };
 
+/*
+Determine if a value is a date
+*/
+$tw.utils.isDate = function(value) {
+	return Object.prototype.toString.call(value) === "[object Date]";
+};
+
 /*
 Iterate through all the own properties of an object or array. Callback is invoked with (element,title,object)
 */
@@ -240,7 +247,7 @@ $tw.utils.parseDate = function(value) {
 				parseInt(value.substr(10,2)||"00",10),
 				parseInt(value.substr(12,2)||"00",10),
 				parseInt(value.substr(14,3)||"000",10)));
-	} else if (value instanceof Date) {
+	} else if ($tw.utils.isDate(value)) {
 		return value;
 	} else {
 		return null;