[wss] /SecurityTokenReference/Reference/@ValueType should be optional

[ronald monzillo <ronald.monzillo@sun.com>]

/SecurityTokenReference/Reference/@ValueType
This required attribute specifies a QName that is used to identify the 
type of token being
referenced (see <wsse:BinarySecurityToken>). This specification does not 
define
any processing rules around the usage of this attribute, however, 
specification for
individual token types MAY define specific processing rules and 
semantics around the
value of the URI and how it is interpreted. If this attribute is not 
present, the URI is
processed as a normal URI.

This attribute should  be optional (or the last sentence must be deleted)