Serializable class doc should link to serialization specification

The class doc of java.io.Serializable mentions the "Java(TM) Object Serialization Specification" in plain text. This should be a link to the actual spec. Now that specs are adjacent to the APIs, this link can be of the form

    <a href="${docRoot}/../specs/serialization/index.html">

(This will need to change if a @spec javadoc tag is implemented at some point.)

In addition, the "(TM)" should be removed. The javadoc header and footer probably have sufficient trademarking information.