Issues with Audio discs with Data disc information

[hannahjones]

We have come across a small number of audio discs that have data discs written on them. So, when such a disk is loaded on to a Mac, aside from the Audio CD another CD image is mounted. This obviously causes the current version of arcCD to fail to read the disk for archiving, as it is unable to unmount the second image. We're trying these on the Windows system too now, but it's an issue that needs to be addressed for Mac as well.