Fixed compiler warnings in MultiRegions.

CMakeLists.txt

cmake/ThirdPartyBoost.cmake

library/LibUtilities/Communication/GsLib.hpp

library/MultiRegions/AssemblyMap/AssemblyMap.cpp

library/MultiRegions/AssemblyMap/AssemblyMapCG2D.cpp

library/MultiRegions/AssemblyMap/AssemblyMapCG3D.cpp

library/MultiRegions/AssemblyMap/AssemblyMapDG.cpp

library/MultiRegions/ContField3DHomogeneous2D.cpp

library/MultiRegions/DisContField1D.cpp

library/MultiRegions/DisContField2D.cpp

library/MultiRegions/DisContField3D.cpp

library/MultiRegions/DisContField3DHomogeneous1D.cpp

library/MultiRegions/DisContField3DHomogeneous2D.cpp

library/MultiRegions/ExpList.cpp

library/MultiRegions/ExpList1D.cpp

library/MultiRegions/ExpList1DHomogeneous2D.cpp

library/MultiRegions/ExpList2D.cpp

library/MultiRegions/ExpList2DHomogeneous1D.cpp

library/MultiRegions/ExpList3D.cpp

library/MultiRegions/ExpList3DHomogeneous1D.cpp