title: c++ test if 2 sets are disjoint
body: <p>I know the STL has <code>set_difference</code>, but I need to just know if 2 <code>set</code>s are disjoint. I've profiled my code and this is slowing my app down quite a bit. Is there an easy way to see if 2 sets are disjoint, or do I need to just roll my own code?</p>
  
  <p>EDIT: I also tried <code>set_intersection</code> but it took the same time...</p>