[patch] mount fails to call external programs

Hello.

The 'mount' program attempts to maintain external mount programs in order to determine whether it needs to call external programs or handle it internally.

Not all external programs can be listed in mount.c.  Indeed, my mount_md failed after mount trying to handle it itself.

The solution is to maintain interally handlable fs types.

I am not fully sure if I listed all of them correctly; however, it fixes the problem.

Thanks,
Hiro