Adding Cuckoo Table SST option to db_bench

Summary: Adding flags to use cuckoo table SST in db_bench.cc

Test Plan: Ran benchmark with fillseq and readrandom

Reviewers: sdong, ljin

Reviewed By: ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D21729
Bump up version

Summary: Bump up version after we've cut 3.4

Test Plan: N/A

Reviewers: yhchiang, ljin

Reviewed By: ljin

Subscribers: leveldb, dhruba, igor

Differential Revision: https://reviews.facebook.net/D22047
Update release note of 3.4

Summary: N/A

Test Plan: N/A

Reviewers: yhchiang, ljin

Reviewed By: ljin

Subscribers: dhruba, leveldb, igor

Differential Revision: https://reviews.facebook.net/D22053
WriteBatchWithIndex: a wrapper of WriteBatch, with a searchable index

Summary:
Add WriteBatchWithIndex so that a user can query data out of a WriteBatch, to support MongoDB's read-its-own-write.

WriteBatchWithIndex uses a skiplist to store the binary index. The index stores the offset of the entry in the write batch. When searching for a key, the key for the entry is read by read the entry from the write batch from the offset.

Define a new iterator class for querying data out of WriteBatchWithIndex. A user can create an iterator of the write batch for one column family, seek to a key and keep calling Next() to see next entries.

I will add more unit tests if people are OK about this API.

Test Plan:
make all check
Add unit tests.

Reviewers: yhchiang, igor, MarkCallaghan, ljin

Reviewed By: ljin

Subscribers: dhruba, leveldb, xjin

Differential Revision: https://reviews.facebook.net/D21381
Adding Column Family support in db_bench.

Summary:
Adding num_column_families flag. Adding support for column families in DoWrite and ReadRandom methods.
[Igor, please let me know if this approach sounds good. I shall add it to other methods too.]

Test Plan: Ran fillseq on 1M keys and 10 Column families and ran readrandom.

Reviewers: sdong, yhchiang, igor, ljin

Reviewed By: ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D21387