Where is org.apache.hadoop.streaming.io.IdentifierResolver defined?

[W.P. McNeill]

I have some 0.20.2 Hadoop code that
extends org.apache.hadoop.streaming.io.IdentifierResolver. That code found
this in the hadoop-*-streaming.jar in the contrib/streaming directory. I am
trying to build it in an environment that only uses jars from 0.20.203.
However I can't find where org.apache.hadoop.streaming.io.IdentifierResolver
is in this version of Hadoop. Which jar now contains this class?