Cocoa: Fix flicker on window resize.

Cocoa: Fix flicker on window resize.

During window resizing the geometry change events
must be processed before returning from the event
handler.

New API: QWindowSystemInterface::handleSynchronousGeometryChange,
similar to handleGeometryChange but sends the event
immediately instead of queueing it.

Change-Id: I7dc809b3fd2e8a933c100fef3f5144972f46e363
Reviewed-on: http://codereview.qt.nokia.com/2993
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Paul Olav Tvete <paul.tvete@nokia.com>