Timeout Notification Signal

[alas]

With idle-timeouts, would like to receive a signal x seconds before timeout occurs. Perhaps as a separate parameter (--idle-timeout-warning=x)?

[Antoine Martin]

Follow up from #803.

[Antoine Martin]

• r8703 adds the grace timeout which can be overriden by hooking the idle_grace_timeout_cb function, by default the client will get a notification message at 90% of the time. The percentage can be changed using the env var XPRA_GRACE_PERCENT.
• r8705 makes us slow down screen updates to just 2 per second when we reach the grace period (the code is reusable)

Ready for testing!

[Antoine Martin]

@sbennett: bump!

[Antoine Martin]

I've been told this works as expected.