Updated Lzop to return the correct decompressor type.

This fixes 

https://github.com/omalley/hadoop-gpl-compression/issues/3

I tested it manually with a word count job that spills more than once in the map and has 1000 reducers.  If you set 

-Dmapreduce.map.output.compress.codec=com.hadoop.compression.lzo.LzopCodec
 
before this change the process will OOM.  After the change it completes successfully.