[screen-devel] Implement dead/zombie window polling

[Alex Naumov]

Hello,

yet another patch in git.

Currently if zombie keys are defined, one needs to explicitly
hit a key to tell screen to try to reconnect a window.
This is rather unfortunte if you for example have dozens of screens
connected to foreign machines through network connections.
Once the network connection is cut for a while, all windows will
enter the dead/zombie state and one has to go through all windows
manually and hit the zombie resurrect key, once the network got
set up again.

This patch implements auto-reconnecting via zombie_timeout
(in seconds) variable. By default it is set to 0 which complies
to current behavior (no polling is done).


Already tested in SLE and openSUSE.
Feel free to test it and answer here if something goes wrong.

Alex