Fixed: CPDatePicker value is wrong when making a click on the stepper

Previously, when making a click on the stepper of a textual CPDatePicker, the intern value of the stepper wasn't updated with the correct value of the CPDatePicker. This occurred when the user changed the dateValue in the delegate methods of the textField.
Fixed: typo in _CPDatePickerTextField.j
Fixed: fixed gangster's comment
Fixed: wrong comment
Fixed: stringValue is used instead of intValue
Merge pull request #2140 from Dogild/DatePickerStepperValue

Fixed: CPDatePicker value is wrong when making a click on the stepper