first rdb commit

Summary: First commit for rdb shell

Test Plan: unit_test.js does simple assertions on most of the main functionality; will update with rest of tests

Reviewers: igor, rven, lijn, yhciang, sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D28749
Merge pull request #413 from saghmrossi/master

first rdb commit