This is a followup to PR/14558.
- itimerfix(9) limited the number of seconds to 100M, before I changed
it to 1000M for PR/14558.
- nanosleep(2) documents a limit of 1000M seconds.
- setitimer(2), select(2), and other library functions that indirectly
use setitimer(2) for example alarm(3) don't specify a limit.
So it only seems appropriate that any positive number of seconds in
struct timeval should be accepted by any code that uses itimerfix(9)
directly, except nanosleep(2) which should check for 1000M seconds
manually. This changes makes the manual pages of select(2), nanosleep(2),
setitimer(2), and alarm(3) consistent with the code.
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