Log Message:
pkgtools/pkglint: update to 20.1.3

Changes since 20.1.2:

Stricter check for Python version numbers. Before, 25 and 26 had not
been marked as wrong.

In assignments like PKGNAME=${DISTNAME:S,from,to,}, modifiers that don't
have any effect generate a note. Most of these modifiers are redundant
or outdated.

Patches must not add well-known absolute paths like /usr/pkg, /var and
/etc since these must be overridable by the pkgsrc user. Other absolute
paths continue to be allowed.