HBase region observer coprocessor not firing from Pig 'store'

When using pig to load data into HBase the region observer coprocessor (specifically prePut() as I have not tested all the other possible region observer combinations) with the 'store' command the coprocessor is not getting invoked.

I have tracked this down and come up with a simple patch. A record of the investigation is on both the Pig and HBase user forums.