Log Message:
pkgtools/pkglint: update to 20.1.15

Changes since 20.1.14:

Fix confusing wording of diagnostic "should contain text".  It's more
precise to say "this line should consist of this text".  Otherwise it's
too easy to interpret it as "the text should occur somewhere in the
line".

Allow BUILDLINK_PREFIX.* to be used in helper files.  Especially for
programming language packages, files like plugin.mk often include
buildlink3.mk and therefore may refer to the BUILDLINK_PREFIX of this
package.

Warn about redundant BUILDLINK_API_VERSION restrictions.  Previously, the
check had only been enabled if the operators from the default dependency
pattern (buildlink3.mk) and the additional dependency pattern (package)
used the same operators, which already covered most practical cases.

Determine SuSE versions from the pkgsrc tree.