Unroll parameter list for FieldVector constructor

Bug Report

The coordinate parameter list at dune/structures/material.hh#89 is not unpacked. Therefore, only a single value is passed to the Dune::FieldVector constructor, leading to an assertion failure. This failure is currently avoided by setting the -DNDEBUG CPP flag, which omits all assert() calls.

Proposal

Unpack the parameter list properly. To be sure that the initializer list constructor is called, add parentheses.

T parameter_unrolled(const Entity& e, int i, T x...) const
{
  return this->parameter(e, Dune::FieldVector<T, dim>({ x... }), i);
}