More Hadoop 2 compatibility fixes

The main code uses ContextUtil to avoid using classes that have changed between Hadoop 1 and Hadoop 2 (e.g. org.apache.hadoop.mapreduce.TaskAttemptContext becoming an interface), but the tests do not, so this PR makes that change so that it's possible to run tests with Hadoop 2. (You have to change the Hadoop version number to do that.)

There are a couple of other small fixes related to using Hadoop 2 and a later version of Pig. All are compatible.