v6.8.2: Fix for empty argv handling.

This release adds a patch from PR#92 to aborting early if argv is not set or
empty.
Nothing else has changed in this patch release.

v6.8.1

• This release fixes one major issue that has been assigned CVE-2019-25016.

  Rules that allowed the user to execute any command would inherit the
  executing users PATH instead of resetting it to a default PATH.
  The path will now be correctly reset (d5acd52) to the defined default PATH.

  Those rules still allow the user to execute any program from their PATH
  but executed commands won't inherit the users PATH anymore.

  Rules that limit the user to execute only a specific command are not affected
  by this and are only executed from the default PATH and with the PATH
  environment variable set to the safe default.

Other changes are:

• apply missing man page changes
• Fixes to the configuration parser 2d7431c, 01ac841 and 36cc28e
• Minor documentation and error message wording changes.

v6.8: This release adds the `nolog` option and a few other minor documentation

changes from upstream. Additionally the configure script and makefile
had some changes to add support for NetBSD, FreeBSD and Mac OS X.

v6.6.1

This release fixes some bugs when parsing /proc/self/stat and adds some more warning/error messages.

v6.6

release 6.6