Currently the iso reading code assumes that the iso file has the Joliet and Rock
Ridge extension on, which can result in errors or bad file names if the iso
dosn't have them.

The way to solve this is that the isoinfo program needs to be run twice. The
first time to see what extensions the iso supports, and the seconds to actually
do the listing/extracting. The problem is that the arguments for the second
program depend on the result from the first program. It seems that the
fr_process_start does not start immideatly but delays it for later execution,
meaning I can't use it to actually get the results I need before setting the
parameters for the second command.

I believe the only way to do this is to create a new FrProcess for getting the
supported iso extensions before using the FrCommand's FrProcess for doing the work.

Is there a more 'correct' way to do this, or is this the right way to do this?