Make GPU hot-add reliable for enabling extra outputs
When a GPU is auto-bound adding more outputs to a screen, that needs to count
as a configuration change on that screen so that a WM listening for
RRScreenChangeNotify gets notified and handles it as a hotplug. This is
particularly for cases where the outputs are already connected. Otherwise
nothing might happen.
Issue #909 (closed) describes a real world case where plugging in a DisplayLink dock
with a monitor already connected is sometimes left inactive by GNOME. That
issue is a race, and requires adding a sleep(5); as the first thing in
NewGPUDeviceRequest() to reproduce reliably. With the sleep, the monitor in the
dock will never activate automatically. Add this fix over the sleep, and the
issue is gone.
This fix was originally developed on a branch replicating Ubuntu 19.04 patch set based on xserver 1.20.4. Testing on master branch was impossible due to #910.
Closes: #909 (closed)