Going to installer:
If you don't have php compiled with mysql support, you get an exception about no valid db driver for mysql. The backtrace suggests that mw-config/index.php calls includes/WebStart.php, which calls SessionManager::getGlobalSession(), which calls SessionManager->generateSessionId(), which calls BagOStuff->get(string), which eventually goes to SqlBagOStuff->getDB(integer), which explodes.
If you do have mysql support compiled in, no exception, but you quickly run into "Your session data was lost! Check your php.ini and make sure session.save_path is set to an appropriate directory. " (I imagine because there is no db set up yet).
Thus preventing me from running the installer.