code: public void modifyColumns(final String tableName, HColumnDescriptor descriptor)
        throws IOException {
      modifyColumn(TableName.valueOf(tableName), descriptor);
    }
docs: Modify an existing column family on a table.  NOTE: this is needed for backwards compatibility
  for the hbase shell.
  
  @param tableName a {@link TableName} object.
  @param descriptor a {@link HColumnDescriptor} object.
  @throws java.io.IOException if any.