FAT12 DOS disk folder support

[AkBKukU]

The current extraction validation process doe not work on disks with folders

[btb]

I noticed this too, and fixed it by using the recursive option to mcopy to just copy the whole filesystem rather than looping over the dir listing.

This also takes care of the problem of the 'head' and 'tail' calls not working right on macos because they are using some gnu-specific features. Also, even after I switched to using 'ghead' and 'gtail' on my system, somehow the tail was still off by one line, so the first file was always missing.