Expose more knobs

Several more rocksdb config parameters now available.  See 'options.go', of
course.  The comments there are taken from the rocksdb source code
('include/rocksdb/options.h').
Apache license for these changes.
Comment out broken options.

The latest RocksDB handles certain options differently (and for the better).
For now, we'll just comment out support for those changed options.  For later,
we should re-implement support.
Comment out broken options.

The latest RocksDB handles certain options differently (and for the better).
For now, we'll just comment out support for those changed options.  For later,
we should re-implement support.