Use System.nanoTime() for timeout calculation

This fixes #150.
Making EntityMapper Public & Providing a way to add specific Partitioner for DefaultEntityManager
Fixing code indentation
Merge pull request #478 from sagarl/a6xissues474_468

Making EntityMapper Public & Providing a way to add specific Partitioner for DefaultEntityManager
Merge branch 'nanotime-lock' of https://github.com/ash2k/astyanax into ash2k-nanotime-lock
Merge pull request #482 from sagarl/ash2k-nanotime-lock

Making timeouts more precise in ColumnPrefixDistributedRowLock
Merge remote-tracking branch 'upstream/master'