Add support of mkisofs

[rick-gnous]

I'm wondering why you only support genisoimage and not mkisofs. Isn't interesting to check if genisoimage is installed, then check for mkisofs (or vice-versa) ? They are basically doing the same thing, and they don't have a lot of difference.

[stgraber]

Patches are welcome, we don't need mkisofs in our normal environment :)