Till now, when a tooltip showed up, the underlying main window lost
keyboard focus (keys + mouse wheel). Users had to click again on the window
to regain this focus.

this patch mainly uses a flag that enables to display a window without
activating it (see msdn doc) plus a bit of cosmetics.

this patch should be backported.
(cherry picked from commit e604141e18e6478581ae253a5bd270cc04391d9c)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>