Log message:
pkg_install: use tabs for indentation, not spaces

Log message:
pkg_install: clean up leading, intermediate and trailing whitespace

Log message:
pkg_install: remove trailing whitespace

Log message:
pkg_install: modern computers can handle words longer than 6 letters

Log message:
pkg_install: add Beer-Ware as default acceptable

Log message:
pkg_install: sync allowed licenses with mk/

Log message:
pkg_install: only enable IPv6 on operating systems that support it

needed for UnixWare, reported by Boyd Lynn Gerber

Log message:
pkg_install: Switch to posix_spawn() on newer macOS.

vfork() no longer works on Monterey and causes serious intermittent issues
when upgrading pkg_install.  Forking the INSTALL and DEINSTALL scripts can
sometimes fail, due to the underlying pkg_add/pkg_delete binaries having
been changed or removed, leaving the system broken with no package tools.

The manual page suggests using posix_spawn() instead and that appears to
work correctly.  The code has been laid out so that it's easy enough to
switch other platforms to posix_spawn() too if required, or for improved
performance, and has been verified to work successfully on SmartOS.

Bump pkg_install version to 20211115.

Log message:
pkg_install: Add an explicit dummy DEINSTALL script.

Even with DEINSTALL_SRC set empty, changes in the pkgsrc infrastructure over
the past few years will now create a dynamic +DEINSTALL script regardless,
and while only containing "exit 0", may have a #! using a shell from \ 
pkgsrc.

This can lead to upgrade issues if that shell happens to be unavailable
while pkg_install is being upgraded.  Creating our own dummy script that
explicitly uses /bin/sh avoids that problem.

Log message:
pkg_install: Update to 20211021.

Apply patch from Michal Maruska in NetBSD/pkgsrc#95 to ensure package files
are correctly cleaned up should the POST-INSTALL script phase fail.