Use runtime detection of XInput 2.1 to disable legacy wheel events

Ensure we fall back to using wheel button events if xinput 2.1
scroll events are not available. Handles lack of xinput 2.1
support in the server or in the input devices drivers.

Task-number: QTBUG-38169
Change-Id: Ie4ad9069f648d0ab02d8f9540ed01ad58fd9e9d8
Reviewed-by: Laszlo Agocs <laszlo.agocs@digia.com>
Cocoa: Fix crash on Combobox popup close.

Regression caused by 0be1c4899c.

The calls to handleCloseEvent/flushWindowSystemEvents
may result in popup window deletion and a stale/null
pointer access.

Get the window type before closing it.

Task-number: QTBUG-38418
Change-Id: I212a56979e0248076e1eb5bf9ede1ff0d424e041
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>