Call X11_handle_configure on first MapNotify

The first MapNotify is eaten by X11_Setup, so we need to call
X11_handle_configure explicitly.

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>
Tell the X server we don't want backing store

Doesn't seem desirable when we're using OpenGL anyway.

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>