Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Add missing newline in last line of file.

Uncovered via: fromcvs vs. svn
Approved by: ed (co-mentor)

Add a suite of regression tests for all the recent changes to `env',
using my own script to handle it. I wrote my own partially because
of all the quoting-issues involved with testing what I wanted to test,
and partially because this lets me commit one script and one data file,
instead of one-file-per-regression-test.

This suite was good enough for my initial testing (and it did help me
find a few bugs that would have otherwise been missed). I'm not sure
how well it will work in general use, but I figured I might as well
commit it. It won't *hurt* to have it available. At the worst, people
can just ignore it.

Approved by: re (blanket `env')