Faster binary search for getColumnLatest

Ran all Phoenix tests.
(TestPhoenixSink hangs, but that is not due to this).

Please have a look. This only helps performance if we do not have to instanceof checks, etc.
Both JDK7 and JDK6 only pas the search term to the right side of the comparator.

With this getColumnLatest no longer shows up in the profiler and I see a 20-30% performance improvement even for small KVs.

Removed the older methods, they weren't used anywhere else. If we need to keep these for backward compatibility we, could add them back.