Phoenix-180

A new pull request with updated comments.  Still trying to test the performance with these changes.
    -> Test cases are not running and all the test cases are failing at the deleteTable sequence.
    -> The checking of the timestamp stored in the table and avoiding concurrent update stats does not work. I am checking on it.
    -> The clearing of the metadata cache should happen in a lock? If so then we need to see every where (even while reading from the cache) we should introduce a new lock.
    -> Estimated byte size() is yet to be added to Ptable
    -> Multi CF is not yet tested.  
    But this would help in getting the review done on the latest changes.