* configure.ac: Check existence of timeout command.

* src/lcopy-update (update): Set default 600 sec as timeout.

* src/lcopy-update (LCOPY_UPDATE_TIMEOUT): Introduce new
parameter in conf.

* src/liblcopy.sh.in (lcopy_backend_call_with_timeout):
New function.
(lcopy_backend_update): Use lcopy_backend_call_with_timeout.

* src/liblcopy_backends.sh.in (lcopy_wait_timed): Removed.
use timeout command in coreutils.