(first_call): Make it private to rpl_nanosleep, and have it
be zero initially as that's a bit faster.
(my_usleep): Round up fractional times instead of truncating them,
as this is the usual meaning for 'sleep'.
Don't use SA_INTERRUPT to decide whether to call sigaction, as
POSIX.1 doesn't require SA_INTERRUPT and some systems
(e.g. Solaris 7) don't define it. Use SA_NOCLDSTOP instead;
it's been part of POSIX.1 since day 1 (in 1988).
Paul Eggert
Jim Meyering