Don't change focus in response to FocusIn events
Previously, when we received a FocusIn event, we would update the input focus,
because client_focus_update set globalconf.focus.need_update to true.
However, this is wrong for clients following the globally active focus model,
because in this case its the client which controls which window has the input
focus. It could happen that we thus took away the focus from the client which
just gave itself the focus.
Signed-off-by: Uli Schlachter <psychon@znc.in>