Leveldb subtree at 1 10 0

This is an improvement on my pull request #2616 . I have made it a separate pull request so that it can be selectively merged.

This incorporates everything in #2616 (bringing leveldb in using git-subtree) and additionally does the following:

- Brings the LevelDB code base up to 1.10.0
- Incorporates an upstream deadlock fix for Windows condition variables

Here's the upstream issue regarding the deadlock:
code.google.com/p/leveldb/issues/detail?id=149

This is the commitlog of the subtree:
https://github.com/vinniefalco/LevelDB/commits/bitcoin-fork