Fixing integer overflows and memory corruption in libbmrm

libbmrm had several problems:
* when the BufSize (size cutting plane buffer) was too small, the first iteration after a "full" buffer yields to memory corruption -- fixed
* ``BufSize * nDim`` could exceed ``size_t::max`` -- fixed
* setting ``m_verbose = true`` enabled expensive debugging information even if DEBUG was not set -- fixed