ok deraadt@

The latest NetBSD (6.1.5) arc4random does not appear to reseed the CRNG state
after a fork, so provide an override until the fork-safe version in CVS appears
in a release.
These are the same as the FreeBSD shims.
ok deraadt@

The FreeBSD-native arc4random_buf implementation falls back to weak sources of
entropy if the sysctl fails. Remove these dangerous fallbacks by overriding
locally.
Unfortunately, pthread_atfork() is also broken on FreeBSD (at least 9 and 10)
if a program does not link to -lthr. Callbacks registered with pthread_atfork()
simply fail silently. So, it is not always possible to detect a PID wraparound.
I wish we could do better.
This improves arc4random_buf's safety compared to the native FreeBSD
implementation.
Tested on FreeBSD 9 and 10.

ok beck

OK: beck@

can avoid reinventing the wheel
ok guenther schwarze

brad and millert, with hints from guenther, jmc, and otto I think.
ok previous.

where applicable.

(this follows FreeBSD and Linux. Single Unix 2 is still illogical)

of the code as a large number of similar clauses makes it impossible
to write an ad for a product using the code...

entire trees for testing anyway, I might as well do this intrusive touching
of include files now.  Added openBSD tags.