compress kv pairs in ParquetInputSplits

Turns out the KV pairs should be compressed as well.

````
2014-04-02 01:47:22,308 [main] ERROR org.apache.pig.tools.grunt.Grunt - ERROR 6017: JobID: null Reason: java.io.UTF
DataFormatException: encoded string too long: 69938 bytes
        at java.io.DataOutputStream.writeUTF(DataOutputStream.java:347)
        at java.io.DataOutputStream.writeUTF(DataOutputStream.java:306)
        at parquet.hadoop.ParquetInputSplit.writeKeyValues(ParquetInputSplit.java:306)
        at parquet.hadoop.ParquetInputSplit.write(ParquetInputSplit.java:170)
        at org.apache.hadoop.io.serializer.WritableSerialization$WritableSerializer.serialize(WritableSerialization
.java:90)
        at org.apache.hadoop.io.serializer.WritableSerialization$WritableSerializer.serialize(WritableSerialization
.java:77)
        at org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigSplit.write(PigSplit.java:263)
````