utils: Clean up and add tests.

* haunt/utils.scm (flat-map, string-split-at): Add docstring.
  (file-name-components): Adjust slightly to handle "/".
  (join-file-name-components): Use prefix string join grammar.
  (absolute-file-name): Add docstring.
* test-env.in: New file.
* tests/utils.scm: New file.
* Makefile.am (TESTS, TEST_EXTENSIONS, SCM_LOG_COMPILER,
  AM_SCM_LOG_FLAGS): New variables.
* configure.ac: Add test-env pre-processed file.
* build-aux/test-driver: New file.

.gitignore

@@ -2,7 +2,6 @@ Makefile
 Makefile.in
 /aclocal.m4
 /autom4te.cache/
-/build-aux/
 /config.log
 /config.status
 /configure
@@ -15,3 +14,8 @@ Makefile.in
 /scripts/haunt
 *.tar.gz
 /website/site
+/test-env
+*.log
+*.trs
+/build-aux/install-sh
+/build-aux/missing