title: A handler conflict occurred. This may disable some commands
body: <p>I want to be able to control when a particular command can be enabled in a toolbar. Currently this is in my <code>plugin.xml</code> file:</p>
  
  <pre><code>&lt;extension
       point="org.eclipse.ui.commands"&gt;
    &lt;command
          defaultHandler="my.plugin.handler.Terminate"
          description="Terminate session"
          id="my.plugin.terminate"
          name="Terminate"&gt;
    &lt;/command&gt;
  &lt;/extension&gt;
  &lt;extension
       point="org.eclipse.ui.commandImages"&gt;
    &lt;image
          commandId="my.plugin.terminate"
          icon="icons/terminate.gif"&gt;
    &lt;/image&gt;
  &lt;/extension&gt;
    &lt;extension point="org.eclipse.ui.menus"&gt;
    &lt;menuContribution locationURI="toolbar:my.plugin.views.RuntimeSessionsView"&gt;
       &lt;command
             commandId="my.plugin.terminate"
             disabledIcon="icons/terminate_dis.gif"
             icon="icons/terminate.gif"
             style="push"&gt;
       &lt;/command&gt;
  &lt;/menuContribution&gt;
  &lt;/extension&gt;
  &lt;extension
       point="org.eclipse.ui.handlers"&gt;
    &lt;handler
          class="my.plugin.handler.Terminate"
          commandId="my.plugin.terminate"&gt;
       &lt;enabledWhen&gt;
          &lt;with
                variable="canTerminate"&gt;
             &lt;equals
                   value="true"&gt;
             &lt;/equals&gt;
          &lt;/with&gt;
       &lt;/enabledWhen&gt;
    &lt;/handler&gt;
  &lt;/extension&gt;
  </code></pre>
  
  <p>And here is what I get in the console:</p>
  
  <pre><code>!ENTRY org.eclipse.ui.workbench 2 0 2015-03-11 11:59:05.237
  !MESSAGE A handler conflict occurred.  This may disable some commands.
  !SUBENTRY 1 org.eclipse.ui.workbench 2 0 2015-03-11 11:59:05.237
  !MESSAGE Conflict for 'my.plugin.terminate':
  HandlerActivation(commandId=my.plugin.terminate,
      handler=my.plugin.handler.Terminate,
      expression=,sourcePriority=0)
  HandlerActivation(commandId=my.plugin.terminate,
      handler=my.plugin.handler.Terminate,
      expression=,sourcePriority=0)
  WARNING 15-03-11,11:59:05 (0) Conflict for 'my.plugin.terminate':
  HandlerActivation(commandId=my.plugin.terminate,
      handler=my.plugin.handler.Terminate,
      expression=,sourcePriority=0)
  HandlerActivation(commandId=my.plugin.terminate,
      handler=my.plugin.handler.Terminate,
      expression=,sourcePriority=0)
    Conflict for 'my.plugin.terminate':
  HandlerActivation(commandId=my.plugin.terminate,
      handler=my.plugin.handler.Terminate,
      expression=,sourcePriority=0)
  HandlerActivation(commandId=my.plugin.terminate,
      handler=my.plugin.handler.Terminate,
      expression=,sourcePriority=0)
  </code></pre>
  
  <p>Currently the <code>my.plugin.terminate</code> command is disabled and I am getting this error message. It would disappear if I would deleted the last extension point ("org.eclipse.ui.handlers"), but then the <code>my.plugin.terminate</code> command would be enabled again. </p>
  
  <p>➤ What I want to achieve is to be able to control the enabled / disabled state of this command. How can I do this?</p>