Ensure that empty directory variables work with empty content variables. This test ensures that, if both $(wheredir) and $(where_HOW) are the empty string, then the `install' and `uninstall' rules behave sanely, for several directory variables `wheredir' and several primaries `HOW'. * tests/instdir.test: New test. * tests/Makefile.am: Update. Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>