Squashed commit of the following:

    fs/nxffs:  Add partial implementation of the truncate method:  It extend files, but cannot yet shrink them.
    fs/smartfs:  Add partial implementation of the truncate method:  It extend files, but cannot yet shrink them.
    fs/fat:  Add partial implementation of the truncate method:  It extend files, but no yet shrink them.
    fs/nfs:  Add support for the truncate method to the NFS file system.