Merge pull request #245 from ForbesLindesay/patch-1

Make `DefaultsError` a real `Error` object

lib/utils.js

@@ -82,9 +82,12 @@ function repeat_string(str, i) {
 };
 
 function DefaultsError(msg, defs) {
+    Error.call(this, msg)
     this.msg = msg;
     this.defs = defs;
 };
+DefaultsError.prototype = Object.create(Error.prototype)
+DefaultsError.prototype.constructor = DefaultsError
 
 DefaultsError.croak = function(msg, defs) {
     throw new DefaultsError(msg, defs);