Log Message:
pkgtools/pkglint: update to 5.6.0

Changes since 5.5.16:

* Check for negated shell commands (if ! test -z "foo"); they are not
  supported by Solaris.

* Don't check variable permissions for infrastructure files. A warning
  like "may not be set by any package" doesn't make sense for them.

* Check that PLIST_VARS matches PLIST.*, which is especially useful in
  options.mk files.

* Improve checks for options.mk files (for PKG_OPTIONS_SET).

* Prefer options handling with !empty() over checking empty() first.

* Prefer ${MACHINE_ARCH} == i386 over !empty(MACHINE_ARCH:Mi386), for
  single-valued variables.