Design decisions

We are using the PCNTL extension to provide parallel execution on *ix. This is not implemented on Windows. In order to make a windows implementaion possible at some stage this is the only *ix specific extension we are using. In some ways this will make the code slower (we have to prapre the tests, write them to disk, run them, write the results to disk... in order to avoid using interprocess communication. This actually makes very little difference to performance because the majority of execution time is spent in running the tests.