Prevent activation of windows with Qt::WindowDoesNotAcceptFocus.

Task-number: QTBUG-32385
Change-Id: I307e2a3e5157b351663940d5d02fc16b3127b5dd
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>
xcb: Don't use Xlib's XBell() function

XBell() just sends a Bell request to the X11 server. This can be done
equally well (and with less ifdefs) through xcb's xcb_bell().

Change-Id: If41d955aa97acfe9e0a8b9fce05c11ebc146ce8e
Signed-off-by: Uli Schlachter <psychon@znc.in>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>