We use the program argv to both find the program to run (argv[0]) and to hold the arguments to the program. Most of the time this is fine, but if we want to let programs specify argv[0] independently (which is possible in standard *NIX programs), this double duty doesn't work. So let's split the path to the program to run out into a separate field by itself. This simplifies the various sim_open funcs too. By itself, this code is more of a logical cleanup than something that is super useful. But it will open up customization of argv[0] in a follow up commit. Split the changes to make it easier to review.