[SPARK-4326] fix unidoc

There are two issues:

1. specifying guava 11.0.2 will cause hashInt not found in unidoc (any reason to force the version here?)
2. unidoc doesn't recognize static class defined in a base class

@aarondav @srowen @vanzin
Interesting that `org.apache.spark.network.protocol.Message` did not have this same problem, as it follows the same pattern.