RFR 9: 8180082 : Broken javadoc links

[Roger Riggs]

Please review corrections to broken javadoc links:
  - links to the serialization spec now in ./specs/serialization
  - links in java.lang to java/util/Spliterator
  - link in ModuleLayer to Classloader
  - Links using ../../../.. do not work well when they show up in some 
indexes; they should use @docRoot

webrev:
   http://cr.openjdk.java.net/~rriggs/webrev-broken-links-8180082/

Issue:
   https://bugs.openjdk.java.net/browse/JDK-8180082

Thanks, Roger