Makefile.am: Move AM tests to `tests/Makefile.am'.

* Makefile.am: Move AM tests to `tests/Makefile.am'.
  (SUBDIRS): Add `tests'.
* tests/Makefile.am: New file.
* configure.ac (AC_CONFIG_FILES): Add `tests/Makefile'.
tests/Makefile.am: Use pre-built files for tests.

* tests/Makefile.am: Use pre-built files from the repository for
  tests instead of installed ones.
  (AM_TESTS_ENVIRONMENT, SCM_LOG_COMPILER): Update.
  (EXTRA_DIST): Add tests.