Log Message:
pkgtools/pkglint: update to 5.6.4

Changes since 5.6.3:

* Allow += for COMMENT

* Sync variable type definitions with reality

* Fix check for "used but not defined" variables. This check had been
  broken since pkgtools/pkglint/files/pkglint.pl r1.776 from 2008-10-18
  (3cd071958e63), which missed its 10-year anniversary by just 9 days.

  After fixing this check, pkglint produces about 800 new warnings
  spread all over pkgsrc, most of which are real typos.

* Detect used variables also in .if and .elif conditions. This is
  closely related to the above fix and reduces the number of "defined
  but not used" variables, while at the same time producing new warnings
  because these variables are used at load time, where some of these
  variables are not yet defined.

* Detect variables for which pkglint doesn't know the exact data type
  by scanning all files under mk/ at startup. Currently there are about
  470 of these variables. No "used but not defined" warnings are issued
  for these variables anymore.

* To speed up pkglint when checking the whole pkgsrc tree at once, the
  most often needed files are cached to reduce IO load. The checks for
  USE_TOOLS are optimized now since they were a major bottleneck.
  Together with other performance improvements this makes pkglint about
  50% faster when checking the whole pkgsrc tree including pkgsrc-wip.