Exception fix for early android versions

Fix for this exception on API versions < 14

0java.lang.NoSuchMethodError: android.widget.FrameLayout.onPopulateAccessibilityEvent
1at net.simonvt.datepicker.DatePicker.onPopulateAccessibilityEvent(DatePicker.java:393)
2at net.simonvt.datepicker.DatePicker.dispatchPopulateAccessibilityEvent(DatePicker.java:387)
3at android.view.ViewGroup.dispatchPopulateAccessibilityEvent(ViewGroup.java:1135)
...