Linking to libpython is unnecessary.  This removes the -fPIC
requirement.

[Tracking bug 21562]

[git-p4: depot-paths = "//depot/software/common/ConsensusCore/": change = 118549]
Add Version::VersionTuple

[Tracking bug 21562]

[git-p4: depot-paths = "//depot/software/common/ConsensusCore/": change = 118557]
Use setS instead of hash_setS for the vertex container type in PoaGraph.

This fixes compilation under boost 1.48.  Benchmarking shows no
performance impact for our use cases.

[Tracking bug 21562]

[git-p4: depot-paths = "//depot/software/common/ConsensusCore/": change = 118558]
Bump version to 0.5.0

[Tracking bug 21562]

[git-p4: depot-paths = "//depot/software/common/ConsensusCore/": change = 118559]