sort(1): Replace NetBSD version with Free/Open version

sort(1): Replace NetBSD version with Free/Open version

With my ongoing collation work, I discovered our sort was not locale
sensitive, but GNU sort was.  I replaced our ancient GNU sort with
NetBSD's version about 4 years ago.  NetBSD hasn't updated that version
since.  However, FreeBSD got rid of their GNU sort fairly recently and
replaced it with another BSD-licensed version.  Four months ago, it was
imported into OpenBSD, they made some corrections which were incorporated
back in FreeBSD in the April timeframe.

This version is locale sensitive and gives the same answers as GNU sort in
my (admittedly) very limited testing.

I fixed some minor issues that GCC5 was squawking about (mainly unused
variables) and I changed the --parallel option PTHREAD_MUTEX_ADAPTIVE_NP
behavior to PTHREAD_MUTEX_ERRORCHECK (the default POSIX behavior).  DF
does not have the former flag implemented.