Switch PageViewEvalFunc's returned schema to tuple

When using current svn's pig, zero_country.pig failed with

  <file zero_country.pig, line 37, column 13> pig script failed to validate: org.apache.pig.impl.logicalLayer.FrontendException: ERROR 0: Given UDF returns an improper Schema. Schema should only contain one field of a Tuple, Bag, or a single type. Returns: {chararray,chararray,chararray}

. We fix the output schema of PageViewEvalFunc to return a tuple.

Change-Id: Iccaed180ebcadcc8896a1e5ba30bc841a5b17af7