[common.fmatrix] added another operator*
[common.fmatrix] added another operator*

This time we allow to multiply a RxC and a 1xC matrix by taking the
transposed of the right matrix. This is mathematically incorrect, of
course, but since a FieldMatrix has no means to be transposed this is it
then.

renemilk/DUNE-Stuff,renemilk/DUNE-Stuff,renemilk/DUNE-Stuff