Get a list of all preordered namespace hashes that haven't expired yet.
    Used for testing

def namedb_get_all_preordered_namespace_hashes( cur, current_block ):
    """
    Get a list of all preordered namespace hashes that haven't expired yet.
    Used for testing
    """
    query = "SELECT preorder_hash FROM preorders WHERE op = ? AND block_number >= ? AND block_number < ?;"
    args = (NAMESPACE_PREORDER, current_block, current_block + NAMESPACE_PREORDER_EXPIRE )

    namespace_rows = namedb_query_execute( cur, query, args )
    ret = []
    for namespace_row in namespace_rows:
        ret.append( namespace_row['preorder_hash'] )

    return ret