important fix: -Wnarrowing, this allows c++0x

fix casting warning/error in swig generated math_py.cpp file, now
c++11 shouldn't fail!

math_py.cpp:6671:47: warning: narrowing conversion of 'self->nta::SparseBinaryMatrix<UI1, UI2>::nCols<unsigned int, unsigned int>()' from 'nta::SparseBinaryMatrix<unsigned int, unsigned int>::nz_index_type {aka unsigned int}' to 'int' inside { } is ill-formed in C++11 [-Wnarrowing]
     int dims[] = { self->nRows(), self->nCols() };
                                               ^