usleep under Vax/Ultrix

[Guy Harris]

>You can also use select with a subsecond sleep.
>
>I don't think System V Release 3 has a subsecond sleep.

S5R3 has "poll()", which can be used to get a subsecond sleep in the
same fashion "select()" is used.

>Probably in SVR4.

S5R4 has "poll()", has a "select()" implemented atop "poll()", and also
has "usleep()" in the BSD compatibility library, presumably implemented
atop "setitimer()" and SIGALRM just as the 4.3BSD version is.