[boost] [graph] a patch for dominator_tree.hpp

Hi all, Recently, I've got few mails concerning about the performance of my dominator tree implementation in the boost graph library, which can be solved by a simple modification. The attached file is my patch on that problem which is based on the most recent version in the subversion repository. Could somebody who has a permission to modify the code apply this patch? The patch has only 5 lines difference and I've double checked it works correctly. Thanks, Jongsoo