Ported db locking code
Ported db locking code

archiecobbs/leveldb,dain/leveldb,maxboehm/leveldb,gaoch023/leveldb-1,cdapio/leveldb,kenwenzel/leveldb,rnarubin/leveldb,zhengkejun/leveldb,kenwenzel/leveldb,mashuai/leveldb,xuzha/leveldb,ljyloo/leveldb