SERVER-15161 RocksCursor::_reverseLocate() Should Seek to Last if can't seek to the key

Closes #767

Signed-off-by: Benety Goh <benety@mongodb.com>
SERVER-15056 Sharded connection cleanup on setup error can crash mongos

Collapse empty if body
SERVER-14964 always collect debug stats if the query log component verbosity is greater than zero
SERVER-15174 Provide some improved semantics for data_cursor and data_view