Has a few annoying problems:
* sleepcmd() -> sleep_main(), the parsing of bad arguments exits the shell.
* sleep_for_duration() in sleep_main() has to be interruptible for
^C traps to work, which may be a problem for other users
of sleep_for_duration().
* BUT, if sleep_for_duration() is interruptible, then SIGCHLD interrupts it
as well (try "/bin/sleep 1 & sleep 10").
* sleep_main() must not allocate anything as ^C in ash longjmp's.
(currently, allocations are only on error paths, in message printing).
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
5e0411a7fb