Add CP::AsgUnionSelectionAlg

...orithms/AsgAnalysisAlgorithms/AsgAnalysisAlgorithmsDict.h

...isAlgorithms/AsgAnalysisAlgorithms/AsgUnionSelectionAlg.h

...AsgAnalysisAlgorithms/AsgAnalysisAlgorithms/selection.xml

...Algorithms/AsgAnalysisAlgorithms/Root/AsgSelectionAlg.cxx

...ithms/AsgAnalysisAlgorithms/Root/AsgUnionSelectionAlg.cxx

...gorithms/src/components/AsgAnalysisAlgorithms_entries.cxx

...ammaAnalysisAlgorithms/python/ElectronAnalysisSequence.py

...EgammaAnalysisAlgorithms/python/PhotonAnalysisSequence.py

...hms/MuonAnalysisAlgorithms/python/MuonAnalysisSequence.py

...ithms/TauAnalysisAlgorithms/python/TauAnalysisSequence.py