setenv() patch for POSIX and memory leak

I have completed a new version[1] of a replacement (kern/99826[1]) for
getenv/setenv/putenv/unsetenv().  A patch against CURRENT that updates
libc and a few base utilities can be found here[2].  I built it and ran
it successfully.

Notes:
1. Fixes memory leak as noted in BUGS section for setenv(3).
    Example of the leak:
    setenv("TZ", "CDT", 1);
    setenv("TZ", "YEKST", 1);  // Leaks
    setenv("TZ", "CDT", 1);
    setenv("TZ", "YEKST", 1);  // Leaks
2. Converts all calls to POSIX from historic BSD API.
    a. unsetenv returns an int.
    b. putenv takes a char * instead of const char *.
    c. errno is set appropriately for POSIX.  Exceptions involve bad
       environ variable and internal initialization code.  These both set
       errno to EFAULT.
3. Several patches to base utilities to handle the POSIX changes are
    from Andrey Chernov's previous commit.  A few I re-wrote to use
    setenv() instead of putenv().  Yes, I dislike putenv().  :)
4. A new regression module to test these functions was written.  It also
    can be used to test the performance.  I found performance to be
    on-par or better.  It is found in tools/regression/environment.
5. Man page could use more work to match all the changes.

Thank you to Andrey and others for your help in proofreading several
iterations of the code.


Sean
   1. http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/99826
   2. http://www.farley.org/freebsd/tmp/setenv/setenv-9/
   3. http://www.farley.org/freebsd/tmp/setenv/setenv-9/setenv.diff
-- 
sean-freebsd_at_farley.org