This is certainly the right thing to do and seems to fix#403. However
I didn't manage to convince myself that this would cause problems for
binomial_heap, given that binomial_heap::erase() calls siftup()
anyway:
void erase(handle_type handle)
{
node_pointer n = handle.node_;
siftup(n, force_inf());
top_element = n;
pop();
}
void increase (handle_type handle)
{
node_pointer n = handle.node_;
siftup(n, *this);
update_top_element();
sanity_check();
}
67d0f9c7df