Makefile.in installs documentation in $prefix/share/doc because $PACKAGE_TARNAME is empty

[neverpanic]

Makefile.in installs documentation in @docdir@, which, when configure is generated with autoconf 2.71 expands to ${datarootdir}/doc/${PACKAGE_TARNAME}.

datarootdir is defined in Makefile.in in line 20, but PACKAGE_TARNAME is never defined. This means that docdir expands to ${datarootdir}/doc/, and make docs installs documentation one level up from where it should be.

I'm not sure how to correctly fix this. Maybe Makefile.in also needs to include PACKAGE_TARNAME = @PACKAGE_TARNAME@, or maybe there's some magic to do in configure.ac to make configure expand this variable?

See also https://trac.macports.org/ticket/67081 and macports/macports-ports#17933.