unused parameter warning in zero_vec

[federkamm]

boost 1.62.0: vec_operations.hpp: line 258 and others cause "unused parameter warnings". The code reads roughly

template <int I> scalar_type read_element(this_vector const & x) {
  return 0;
}

where x is unused.

Plese either remove x from the parameter list:

... read_element(this_vector const &) { ... }

or declare as unused

... read_element( ... ) {
  (void)x;
  return 0;
}

[zajo]

Thanks -- done, see latest develop branch.