Add Tests that employ Lambdas

[ajtack]

At the time of this writing, Riak-cpp relies entirely on traditional functions (with std::bind, for instance) to react to various operations. This is due to the original goal of first-class g++ v4.4 support. However, we need to explicitly target these new technologies.

Acceptance Criteria

• Every riak operation has a passing test employing a lambda instead of std::bind.
• All tests employing lambdas are guarded (#ifndef) for a compatible compiler (>= g++-4.4)
• The documentation is updated to prefer lambda syntax.