public static NFSFileVec make(File f, Futures fs) {
    if( !f.exists() ) throw new IllegalArgumentException("File not found: "+f.toString());
    long size = f.length();
    Key k = Vec.newKey(PersistNFS.decodeFile(f));
    // Insert the top-level FileVec key into the store
    NFSFileVec nfs = new NFSFileVec(k,size);
    DKV.put(k,nfs,fs);
    return nfs;
  }
public static NFSFileVec make ( File f , Futures fs ) { if ( ! f . exists ( ) ) throw new IllegalArgumentException ( "File not found: " + f . toString ( ) ) ; long size = f . length ( ) ; Key k = Vec . newKey ( PersistNFS . decodeFile ( f ) ) ; NFSFileVec nfs = new NFSFileVec ( k , size ) ; DKV . put ( k , nfs , fs ) ; return nfs ; }
Make a new NFSFileVec key which holds the filename implicitly.  This name
is used by the Chunks to load data on-demand.
@return  A NFSFileVec mapped to this file.