hw/xwin: More closely follow ICCCM for setting input focus

hw/xwin: More closely follow ICCCM for setting input focus

In multiwindow mode, more closely follow ICCCM section 4.1.7 when setting X
input focus to a window when the native Windows window acquires input focus:

- If InputHint is FALSE, don't use XSetInputFocus()
- If the window supports the WM_TAKE_FOCUS protocol, send a WM_TAKE_FOCUS message

This helps JDK 1.7 clients acquire the focus correctly.

Also, factor out checking client support for a given WM_PROTOCOLS protocol as a
separate function.

Signed-off-by: Jon TURNEY <jon.turney@dronecode.org.uk>
Reviewed-by: Colin Harrison <colin.harrison@virgin.net>