xsel: Make sure to flush XSetSelectionOwner
xsel: Make sure to flush XSetSelectionOwner

In the atspi2 use case, we do not directly use XPending or XNextEvent
since we let the core select on the X fd. The XSetSelectionOwner request
would then wait for the next incoming message, thus coming completely
out of sync, and disturbing the clipboard management.

brltty/brltty,brltty/brltty,brltty/brltty,brltty/brltty,brltty/brltty,brltty/brltty