AccountHandle could benefit from specialization for std::numeric_limits

Searching for keyed data in containers, such as Boost indices, could be made easier and simpler if AccountHandle had a specialization that permitted its use with std::numeric_limits::min() and std::numeric_limits::max().

The specialization is, in fact, currently assumed to be present by the Pollaris contract and its absence is resulting in incorrect tallying since the introduction of AccountHandle.