Add new multiply Faust::MatSparse member functions and a unit test.

misc/test/CMakeLists.txt

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

src/algorithm/factorization/faust_GivensFGFTParallel.hpp

src/faust_linear_operator/CPU/faust_MatSparse.h

src/faust_linear_operator/CPU/faust_MatSparse.hpp

src/faust_linear_operator/CPU/faust_TransformHelper.h