Instead of trying to start a single driver and bailing out if that fails, try to initialise one by one and use the first one which succeeds.
This should fix problems on machines with no sound card, where -s null had to be specified manually.
This results in shorter and hopefully easier to maintain files.
Note: I had to change paths in #include statements of some unrelated files, because I added the ottd base directory to the include path (-I.)
bjarni