Merge pull request #2 from p2t2/DEV2.1

Will this screw things up?
Added belief propagation, fixes to MH for references, and allow sets to
be registered in universes
Merge remote-tracking branch 'upstream/DEV2.1' into DEV2.1
Added BP test
Added One Time, Any time versions of BP, and MPE BP.
Fixed Dependent  universe test in BP
Merge remote-tracking branch 'upstream/DEV2.1' into DEV2.1
BP merged with lazy factors
Added comments to BP
Merge pull request #94 from bruttenberg/DEV2.1

BP Merge