reap children faster

reap children faster

udevd's event_queue_manager loop is pretty sensitive to the
delays of exiting child processes. I found that it helps boot
times if we try to reap children as quickly as possible.

This patch changes event_queue_manager to call sigchilds_waiting
if it finds a signal has been received.

Signed-off-by: Olaf Kirch <okir@suse.de>