title: How to move tip tag on Mercurial repository
body: <p>I'd like to move the "tip" tag to revision 272 on the following graph. Is it possible without commiting on that head?</p>
  
  <pre><code>o  changeset:   273:40cf2237a3d5
  |  bookmark:    push-notification
  |  tag:         tip
  |  parent:      271:3640ade1df38
  |  user:        xxxxxxxxx &lt;xxxxx@zzzz.com&gt;
  |  date:        Mon May 12 16:11:01 2014 -0300
  |  summary:     Lorem
  |
  | @  changeset:   272:70f0a3f3b74a
  | |  parent:      269:b125e398bd69
  | |  user:        yyyyyyyy &lt;yyyyyyy@zzzzz.com&gt;
  | |  date:        Fri May 09 17:58:35 2014 -0300
  | |  summary:     Ipsum
  | |
  o |  changeset:   271:3640ade1df38
  | |  user:        yyyyyyyy &lt;yyyyyyy@zzzzz.com&gt;
  | |  date:        Fri May 09 17:58:35 2014 -0300
  | |  summary:     Dolor
  | |
  o |  changeset:   270:d064bf9ffad6
  | |  parent:      268:01563b587c71
  | |  user:        xxxxxxxxx &lt;xxxxx@zzzz.com&gt;
  | |  date:        Fri May 09 11:00:47 2014 -0300
  | |  summary:     Sit
  | |
  | o  changeset:   269:b125e398bd69
  | |  parent:      267:602390d3eeb1
  | |  user:        xxxxxxxxx &lt;xxxxx@zzzz.com&gt;
  | |  date:        Fri May 09 08:13:06 2014 -0300
  | |  summary:     Amet
  | |
  o |  changeset:   268:01563b587c71
  |/   user:        xxxxxxxxx &lt;xxxxx@zzzz.com&gt;
  |    date:        Tue May 06 17:47:32 2014 -0300
  |    summary:     Consectur
  |
  o  changeset:   267:602390d3eeb1
  |  user:        yyyyyyyy &lt;yyyyyyy@zzzzz.com&gt;
  |  date:        Fri May 02 14:24:29 2014 -0300
  |  summary:     Abc
  |
  </code></pre>