Enable parallel-tests test driver for the old testsuite.

Enable parallel-tests test driver for the old testsuite.

* configure.ac: New configure test to find out whether `make'
supports order-only prerequisites; set @ORDER@ accordingly.
(AM_INIT_AUTOMAKE): Enable parallel-tests option.
* tests/defs.m4sh (prefix): Derive install prefix for tests
from the test name, to avoid clashes.
* Makefile.am (CXX_TESTS, F77_TESTS, FC_TESTS, COMMON_TESTS):
Reformat.  Adjust for renamed tests.  Add dependencies between
the respective log files of the tests, to ensure proper ordering.
Use order-only dependencies if possible, between test groups that
use the same directory.
(clean-local-legacy): Remove `_inst-*' directories as well.
Prompted by suggestion from Bob Friesenhahn.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>