Add some constructor overloads for GetRequest.

It's always been a bit unfortunate that GetRequest had such a different
API compared to other RPCs.  This is an attempt to try to unify things.
Upgrade to async 1.4.0.
Add a couple integration tests covering NoSuchColumnFamilyException.
Fix distclean: remove com/google/protobuf from the build directory.
Make sure we compile for Java 6.
Update NEWS for the v1.5.0 release.
Upgrade to Netty 3.7.0.