Add an Avro dependency to REPL to make it compile with Hadoop 2

Without this, I was getting the following compilation error:
```
error: error while loading Path, Missing dependency 'class org.apache.avro.reflect.Stringable', required by /Users/mbautin/.m2/repository/org/apache/hadoop/hadoop-common/2.0.0-cdh4.1.2/hadoop-common-2.0.0-cdh4.1.2.jar(org/apache/hadoop/fs/Path.class)
/wd/spark/repl/src/main/scala/spark/repl/ExecutorClassLoader.scala:37: error: org.apache.hadoop.fs.Path does not have a constructor
          fileSystem.open(new Path(directory, pathInDirectory))
```