Switching from Automatic to Manual redirect needs to unmap/remap

When changing a window from automatic redirection to manual redirection, the
parent clip list needs to be recomputed; the easy way to get that computed
right is to unmap/map the window, just as when redirecting the window the
first time.

Thanks to Owen Taylor for helping diagnose this.

Signed-off-by: Keith Packard <keithp@keithp.com>