Automake "strongly discourages" use of the serial driver, and switching
to the preferred parallel driver allows make -j4 check to run in about
half the time on a four core (not thread) host.
* Makefile.am (TESTS, TESTS_ENVIRONMENT): run ./check-guile from
test-suite/, not here.
* check-guile.in: let test harness handle progress output.
* configure.ac (AM_INIT_AUTOMAKE): allow parallel testing.
* test-suite/Makefile.am (SCM_TESTS): remove non-tests.
(EXTRA_DIST): move non-tests here.
(TESTS): include SCM_TESTS (now driven from here).
(TEST_EXTENSIONS): allow customization for .scm and .test.
(TESTS_ENVIRONMENT): stop defining (user only).
(AM_TESTS_ENVIRONMENT): replaces TESTS_ENVIRONMENT; drop guile.
(SCM_LOG_COMPILER): run .scm tests via meta/guile.
(AM_SCM_LOG_FLAGS): keep --no-auto-compile for .scm tests.
(TEST_LOG_DRIVER): run .test tests via custom automake ./driver.
* test-suite/driver: add automake test driver.
