'Extract page limits (start and limit) from GET vars
@param get_vars: the GET vars
@param default_limit: the default limit, explicit value or:
0 => response.s3.ROWSPERPAGE
None => no default limit'

@staticmethod
def _limits(get_vars, default_limit=0):

    start = get_vars.get('start', None)
    limit = get_vars.get('limit', default_limit)
    if isinstance(start, list):
        start = start[(-1)]
    if isinstance(limit, list):
        limit = limit[(-1)]
    if limit:
        if (isinstance(limit, basestring) and (limit.lower() == 'none')):
            limit = None
        else:
            try:
                start = (int(start) if (start is not None) else None)
                limit = int(limit)
            except (ValueError, TypeError):
                (start, limit) = (None, default_limit)
    else:
        start = None
        limit = default_limit
    return (start, limit)
