Added a rudimentary testsuite for herd.

It just includes a few of the ARM and PPC tests from
<http://diy.inria.fr/cats/arm-tests.tgz> and
<http://diy.inria.fr/cats/power-tests.tgz>. I updated the Makefile
with two new targets: `make baseline` regenerates the baselines
(which are stored in testsuite/ARM_results_baseline.txt and
testsuite/PPC_results_baseline.txt) and `make test` runs new tests
and uses mcompare to compare them against the baselines. Also, I
arranged that `make clean` removes the results of the new tests.