Mv fadvise control 2.0

This is the customer requested feature first merged into 1.4.4.  Copied here for 2.0 integration.  

Notes on the feature are here:  https://github.com/basho/leveldb/wiki/mv-fadvise-control  

Notes from 1.4.4 pull request are here:  https://github.com/basho/leveldb/pull/110