RFE: make mount more flexible

[i30817]

'mount.exe' can already simulate parts of imgmount, but 2 crucial parts are missing to be able to flatten all disc images into the native filesystem (well those whose games don't read sectors directly anyway).

1. Mounting multiple directories in the same drive, using the 'disc change' mechanism of dosbox. This is necessary for multidisc games to be able to use this.
2. Mounting a cue extension that has a folder as a track and audio files, just like imgmount. This is necessary for games with cd audio.

These two features would 'close the gap'.

As for why do i want them, it's simple. I want to share data with scummvm and DOS. To do this the ideal mechanism is hardlinks, since the data is all readonly, only if the data is hidden away in a cue/bin or iso in the DOS side, this is impossible.

Another, maybe better, way would be making scummvm read isos/cue/bin inside a game dir for data, but that was suggested and rejected (I think). If someone appeared with a patch ready that had no effort for those guys, maybe, but i kind of fear they'd reject it because it 'would be for piracy' when it's actually just for data compression and less effort.