- when the ratio returned by an attempt of a move is infinite,
previous code was just throwing TRIQS_RUNTIME_ERROR.
- Now when the ratio is infinite, it is replaced by a large number
(>1 is enough for metropolis), and the sign is properly updated
using std::signbit.
- NB :
- a double/float in C++ can be : normal/ zero/ nan/ infinite / subnormal.
Here, the code will recover only from infinite case.
- std::signbit works for infinite (according to standard).