Uh, fix very subtle bug: cxx thought that this line

Uh, fix very subtle bug: cxx thought that this line
		n_pols_to(dim+1, 0)
had the signature
  std::vector<T>::vector (InputIterator, InputIterator, Allocator)
Why? Because both args are (signed) integers, and it wanted to convert
these to pointers, rather than the first to size_t and the second to
T=unsigned int. Fix this by using the fact that the zero initializer
is implied when omitted, so just leave the size of the array.

git-svn-id: https://svn.dealii.org/trunk@5929 0785d39b-7218-0410-832d-ea1e28bc413d