Don't allow multi's to over run the max result size.

The HBase region server will now send a chunk of get responses to a client if the total response size is too large. This will only be done for clients 1.2.0 and beyond. Older clients by default will have the old behavior. This patch is for the case where the basic flow is like this: I want to get a single column from lots of rows. So I create a list of gets. Then I send them to table.get(List<Get>). If the regions for that table are spread out then those requests get chunked out to all the region servers. No one regionserver gets too many. However if one region server contains lots of regions for that table then a multi action can contain lots of gets. No single get is too onerous. However the regionserver won't return until every get is complete. So if there are thousands of gets that are sent in one multi then the regionserver can retain lots of data in one thread.