Minor fixes about C++ namespaces.

misc/test/src/C++/faust_matsparse_mul.cpp.in

misc/test/src/C++/unit/test_Vect_min.cpp.in

src/algorithm/factorization/faust_WHT.h

src/algorithm/factorization/faust_WHT.hpp

src/faust_linear_operator/CPU/faust_MatDense.h

src/faust_linear_operator/CPU/faust_MatDense.hpp

src/faust_linear_operator/CPU/faust_MatSparse.h

src/faust_linear_operator/CPU/faust_TransformHelper.h

src/faust_linear_operator/CPU/faust_Vect.h