Improve synchronization between the parent and children. This fixes
a spurious test failure spotted by anton@ and eliminates sleeping
in the test.

Feedback and OK anton@

To make debugging the kqueue test easier, always print the assertion
failure before returning.

When passing the (1ULL << 32) to EV_SET, it gets casted to __uintptr_t.
On 32 bit architectues, the high bit is lost and the test fails.
Create an invalid pid in the lower 32 bits.
OK guenther@

Prevent silly states via knotes on pids > 2^32 and on nonexistent signals.

ok tedu@

Last parameter to execl[e]() functions *must* be cast to a pointer.
Just NULL is not good practise as NULL is theoretically allowed to
be an integer rather than a pointer.

Use (char *)NULL consisten

Last parameter to execl[e]() functions *must* be cast to a pointer.
Just NULL is not good practise as NULL is theoretically allowed to
be an integer rather than a pointer.

Use (char *)NULL consistently instead of scattering a few (char *)0
and (void *)NULL into the mix.

Prompted by and probably ok deraadt@ millert@ kettenis@

Definitely ok mestre@ ratchov@

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NOTE_FORK|NOTE_TRACK knote can track grandchild processes. Wait for
both child/grandchild process events.

Kill a useless assignment.

Refactor to prepare a future change; no functional changes.

Confirm that a NOTE_EXIT knote is delivered when the child exits
Fix a C thinko

various cleanups; david says results are same

-Wall and calc fix in the random

kill err(3) newlines; ok miod@, deraadt@

A start for testing EVFILT_PROC, not done yet, but this is a good check point.