Fix Model.prototype.inspect

Return the raw object data when running on Node v0.11.14+
That way all `inspect` options are always preserved.

When running on older version:
 - Honour the depth argument passed to the custom `inspect` function.
 - Disable color output, becase there is now way how to detect whether
   colors were enabled or disabled by the top-level caller.

lib/model.js

@@ -438,8 +438,28 @@ ModelBaseClass.prototype.reset = function () {
   }
 };
 
-ModelBaseClass.prototype.inspect = function () {
+// Node v0.11+ allows custom inspect functions to return an object
-  return util.inspect(this.__data, false, 4, true);
+// instead of string. That way options like `showHidden` and `colors`
+// can be preserved.
+var versionParts = process.versions.node
+  .split(/\./g).map(function(v) { return +v; });
+
+var INSPECT_SUPPORTS_OBJECT_RETVAL =
+ versionParts[0] > 0 ||
+ versionParts[1] > 11 ||
+ (versionParts[0] === 11 && versionParts[1] >= 14);
+
+ModelBaseClass.prototype.inspect = function (depth) {
+  if (INSPECT_SUPPORTS_OBJECT_RETVAL)
+     return this.__data;
+
+  // Workaround for older versions
+  // See also https://github.com/joyent/node/commit/66280de133
+  return util.inspect(this.__data, {
+    showHidden: false,
+    depth: depth,
+    colors: false
+  });
 };
 
 ModelBaseClass.mixin = function (anotherClass, options) {

test/validations.test.js

@@ -486,6 +486,14 @@ describe('validations', function () {
         .should.equal('`prop` is invalid (value: [ { a: [Object] } ]).');
     });
 
+    it('should exclude colors from Model values', function() {
+      var obj = new User();
+      obj.email = 'test@example.com';
+      var err = givenValidationError('user', obj, 'is invalid');
+      getErrorDetails(err).should.equal(
+        '`user` is invalid (value: { email: \'test@example.com\' }).');
+    });
+
     function givenValidationError(propertyName, propertyValue, errorMessage) {
       var jsonVal = {};
       jsonVal[propertyName] = propertyValue;