multi-threaded run-tests.php

Hi, Recently we have moved http://gcov.php.net to a new (and much faster) server. This allowed us to reduce the time to build all branches to "just" 2 days (compared with almost one week that would take previously). However I'm still not happy :P The server has 2x2 CPU cores and I would like to use them :) Currently I can speed-up the make process, because it can be parallelized (with -j xx). But the major time is still spent with run-tests.php. So, what I would like to propose is a multi-threaded version of run-tests.php. We could spawn x processes (configurable) and one of them would test y extensions (I think it's better to have each extension's tests tested serially or they may break, because they may use the same resources: BDs, files, etc..). Any comments? Thanks, Nuno