Testing machine descriptions

[DJ Delorie]

I've thought about making a dejagnu testsuite specifically for helping
with new ports, which would mean lots of md-specific tests, but
really, the main testsuite probably covers everything you'd need to
test.  All patches are supposed to be regression tested anyway, which
means running the full dejagnu testsuite before and after your change,
to make sure you didn't break anything.