Spike to create a parallel_test type that optionally pulls test_suffix from env variable.

I'm looking for comments on how this could be useful to the parallel_tests project.  I originally attempted to have it support our minispec test suite, but realized with a few tweaks it could be made to serve about anything.  You could combine my patch with the PARALLEL_TESTS_EXECUTABLE variable and run about anything you could imagine.

For our minispec suite, we had *_spec.rb files under a test folder and we didn't need to load any test unit stuff in run_tests.  This way i just run

PARALLEL_TEST_SUFFIX=*_spec.rb parallel_test -t env ./test

Since this is a spike, i didn't get too crazy with the testing, but it would seem that it should be able to support all the ParallelTests::Test:Runner specs.

So, just wondering how insane you think this is, and how i could modify it to better suite your vision of the project.