Returns the appropriate Manager class for a given Model class.  It does this by
    looking in the boto config for a section like this::
    
        [DB]
        db_type = SimpleDB
        db_user = <aws access key id>
        db_passwd = <aws secret access key>
        db_name = my_domain
        [DB_TestBasic]
        db_type = SimpleDB
        db_user = <another aws access key id>
        db_passwd = <another aws secret access key>
        db_name = basic_domain
        db_port = 1111
    
    The values in the DB section are "generic values" that will be used if nothing more
    specific is found.  You can also create a section for a specific Model class that
    gives the db info for that class.  In the example above, TestBasic is a Model subclass.

def get_manager(cls):
    """
    Returns the appropriate Manager class for a given Model class.  It does this by
    looking in the boto config for a section like this::
    
        [DB]
        db_type = SimpleDB
        db_user = <aws access key id>
        db_passwd = <aws secret access key>
        db_name = my_domain
        [DB_TestBasic]
        db_type = SimpleDB
        db_user = <another aws access key id>
        db_passwd = <another aws secret access key>
        db_name = basic_domain
        db_port = 1111
    
    The values in the DB section are "generic values" that will be used if nothing more
    specific is found.  You can also create a section for a specific Model class that
    gives the db info for that class.  In the example above, TestBasic is a Model subclass.
    """
    db_user = boto.config.get('DB', 'db_user', None)
    db_passwd = boto.config.get('DB', 'db_passwd', None)
    db_type = boto.config.get('DB', 'db_type', 'SimpleDB')
    db_name = boto.config.get('DB', 'db_name', None)
    db_table = boto.config.get('DB', 'db_table', None)
    db_host = boto.config.get('DB', 'db_host', "sdb.amazonaws.com")
    db_port = boto.config.getint('DB', 'db_port', 443)
    enable_ssl = boto.config.getbool('DB', 'enable_ssl', True)
    sql_dir = boto.config.get('DB', 'sql_dir', None)
    debug = boto.config.getint('DB', 'debug', 0)
    # first see if there is a fully qualified section name in the Boto config file
    module_name = cls.__module__.replace('.', '_')
    db_section = 'DB_' + module_name + '_' + cls.__name__
    if not boto.config.has_section(db_section):
        db_section = 'DB_' + cls.__name__
    if boto.config.has_section(db_section):
        db_user = boto.config.get(db_section, 'db_user', db_user)
        db_passwd = boto.config.get(db_section, 'db_passwd', db_passwd)
        db_type = boto.config.get(db_section, 'db_type', db_type)
        db_name = boto.config.get(db_section, 'db_name', db_name)
        db_table = boto.config.get(db_section, 'db_table', db_table)
        db_host = boto.config.get(db_section, 'db_host', db_host)
        db_port = boto.config.getint(db_section, 'db_port', db_port)
        enable_ssl = boto.config.getint(db_section, 'enable_ssl', enable_ssl)
        debug = boto.config.getint(db_section, 'debug', debug)
    elif hasattr(cls, "_db_name") and cls._db_name is not None:
        # More specific then the generic DB config is any _db_name class property
        db_name = cls._db_name
    elif hasattr(cls.__bases__[0], "_manager"):
        return cls.__bases__[0]._manager
    if db_type == 'SimpleDB':
        from sdbmanager import SDBManager
        return SDBManager(cls, db_name, db_user, db_passwd,
                          db_host, db_port, db_table, sql_dir, enable_ssl)
    elif db_type == 'PostgreSQL':
        from pgmanager import PGManager
        if db_table:
            return PGManager(cls, db_name, db_user, db_passwd,
                             db_host, db_port, db_table, sql_dir, enable_ssl)
        else:
            return None
    elif db_type == 'XML':
        from xmlmanager import XMLManager
        return XMLManager(cls, db_name, db_user, db_passwd,
                          db_host, db_port, db_table, sql_dir, enable_ssl)
    else:
        raise ValueError, 'Unknown db_type: %s' % db_type