tests: reorganize and extend tests on aclocal search path(s)

tests: reorganize and extend tests on aclocal search path(s)

* tests/aclocal-search-path.tap: New test, supersedes and
subsumes ...
* tests/aclocal9.test: ... this test ...
* tests/acloca11.test: ... and this one ...
* tests/acloca12.test: ... and this one ...
* tests/aclocal-acdir.test: ... and this one ...
* tests/aclocal-path-nonexistent.test: ... and this one ...
* tests/aclocal-path-precedence.test:: ... and this one ...
* tests/aclocal-path.test: ... and this one ...
* tests/dirlist-abspath.test: ... and this one ...
* tests/dirlist.test: ... and this one ...
* tests/dirlist2.test: ... and this one, all of which have
accordingly been removed.
* tests/list-of-tests.mk: Update.