Log Message:
pkgtools/pkglint: update to 5.6.10

Changes since 5.6.9:

* ALTERNATIVES files are correctly checked now. Before, pkglint had
  suggested to remove the @PREFIX/ from the alternative, which was
  wrong and simply didn't work.

* Diagnostics about variable assignments are ordered to report the
  left-hand side first and then everything to the right of the
  assignment operator.

* The pkglint output is escaped properly to avoid sending unwanted
  escape sequences to the terminal.

* The items in .for loops are parsed taking "double" and 'single'
  quotes into account since bmake does it in the same way since 2015.

* In DESCR files, overly long lines are only warned about if they
  contain a space and therefore can be made shorter.

* In DESCR files, text like ${PREFIX} only gets a note if it refers
  to a commonly known pkgsrc variable. This avoids distraction when
  a package mentions ${prefix}/bin or ${template.property}.

* Lots of refactorings and small changes.