title: git see entire merge diff
body: <p>I want to be able to see the entire patch applied by a merge as a single diff output. In bzr this is the standard (such that if you view the diff at a merge point you get the entire diff resulting from that merge). In git I don't see how to get this unified view of the merge. Using gitk I have to click on each individual commit in the branch. I want to see the entire branch as a single commit.</p>
  
  <p>I know that I can simply manually find the branch point and do a diff between two points, but this is error prone. How can I see the entire diff for a merge?</p>