SERVER-15296 Hook up RocksSortedDataImpl with SortedDataInterface test harness

This commit includes number of changes:
* Hook up RocksSortedDataImpl to sorted data interface tester
* Bunch of fixes in RocksSortedDataImpl. I'm not sure of some of the semantics since there is no interface documentation, but this seems to pass the unit tests. I'm waiting for the clarification here: https://groups.google.com/forum/#!topic/mongodb-dev/pvpCXNbe2KM
* Fix some compile issues due to upstream changes
* Fix RocksRecoveryUnit according to documentation in RecoveryUnit
* Add .clang-format file to rocks root dir, which will help us style our code
* Fix rocks_sorted_data_impl_test
How about adding it to the top level .gitignore?

https://github.com/mongodb/mongo/blob/master/.gitignore