Upgrade LevelDB to 1.14.0

LevelDB 1.14.0 changed the sstable extensions from sst to ldb. The old sst extension is still going to be recognised. 

See 1.14.0 change log on the link bellow:
https://code.google.com/p/leveldb/source/detail?r=0b9a89f40efdd143fa1426e7d5cd997f67ba6361