review request: HBASE-4508 Backport HBASE-3777 (connection sharing) to 0.90 branch

[Ted Yu]

Hi,
I have reviewed latest patch for HBASE-4508 and run test suite.

Jonathan has made good progress in his offline .META. builder whose 0.90
patch is blocked by the integration of HBASE-4508.

rocketfuel has been running 0.90 with HBASE-4508 for 5 months. I feel we
should integrate HBASE-4508 into 0.90.5 soon.

Please provide your comments.

Thanks