dix: Add optional terminate delay

When the command line option "-terminate" is used, it could be
interesting to give it an optional grace period to let the Xserver
running for a little longer in case a new connection occurs.

This adds an optional parameter to the "-terminate" command line option
for this purpose.

v2: Use a delay in seconds instead of milliseconds
    (Martin Peres <martin.peres@mupuf.org>)
v3: Clarify man page entry, ensure terminateDelay is always >= 0,
    simplify TimerFree(). (Peter Hutterer <peter.hutterer@who-t.net>)

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
5 jobs for xfixes-ignore-client in 7 minutes and 31 seconds (queued for 1 second)