title: git log foo..bar -- how to see *merge dates* for changesets?
body: <p>Is it possible to get 'git log' to give the date <em>when a changeset landed on a branch</em> rather than the date when the changeset was created? 'git log --graph' (example truncated output below) gives me much of what I want, but it still prints the dates when the individual changesets were created rather than when they were merged into this branch.</p>
  
  <pre><code>*   commit 7e8d68fc58b915cc17bca41be833c4f7a062cd3c
  |\  Merge: 1b4f10d af0dcdd
  | | Date:   Wed Apr 25 17:40:16 2012 +0100
  | |     Merge branch 'foo'
  | * commit af0dcdd078197a852fcfad11c5111aa11579aa05
  | | Date:   Wed Apr 25 17:36:50 2012 +0100
  | |     t2: adding lorem ipsum again
  | * commit 569f5de0eb40cbf198771812f9b099cf71b5b056
  | | Date:   Wed Apr 25 17:36:36 2012 +0100
  | |     t1: adding lorem ipsum
  * | commit 1b4f10d3eea7c9c6304f7b1fd41818b932e4dad0
  | | Date:   Wed Apr 25 17:38:24 2012 +0100
  | |     t4: fi fo fa fum x 2
  * | commit d25fa0359fbe655b6a4adeb6225ac283b3543ece
  |/  Date:   Wed Apr 25 17:38:10 2012 +0100
  |       t3: fi fo fa fum
  * commit d3239b3e327f740fc7194ecf164538361f715ab5
    Date:   Wed Apr 25 17:34:50 2012 +0100
  </code></pre>
  
  <p>In the above the output is from the <code>master</code> branch. t1 and t2 were created on the <code>foo</code> branch; t3 &amp; t4 were created on <code>bar</code>. Then <code>bar</code> was merged into <code>master</code> followed by merging <code>foo</code> into master.</p>