Fix and enhance decoding of sched_[gs]etaffinity syscalls

Fix and enhance decoding of sched_[gs]etaffinity syscalls

Print cpu_set_t as a set of integers, similar to the way
fd_set is printed as a set of descriptors.

* affinity.c: Include <sched.h>.
(get_cpuset_size): New function.
(print_affinitylist): Rewrite using get_cpuset_size and next_set_bit.
(sched_getaffinity, sched_setaffinity): Print first two args as ints.
* NEWS: Mention this enhancement.
* tests/sched_xetaffinity.c: New file.
* tests/sched_xetaffinity.test: New test.
* tests/Makefile.am (check_PROGRAMS): Add sched_xetaffinity.
(TESTS): Add sched_xetaffinity.test.
* tests/.gitignore: Add sched_xetaffinity.

Reported-by: Joe Korty <joe.korty@ccur.com>