title: Checkbox input using python mechanize
body: <p>I want to fill a form using python mechanize. form looks like:</p>
  
  <pre><code>&lt;POST https://10.20.254.39/cloud_computing/vmuser/migrate_vm/cli multipart/form-data
    &lt;TextControl(vm=cli)&gt;
    &lt;TextControl(chost=10.20.14.39)&gt;
    &lt;SelectControl(dhost=[*, 28, 27])&gt;
    &lt;CheckboxControl(live=[on])&gt;
    &lt;CheckboxControl(undefinesource=[on])&gt;
    &lt;CheckboxControl(suspend=[on])&gt;
    &lt;SubmitControl(&lt;None&gt;=Submit) (readonly)&gt;
    &lt;HiddenControl(_formkey=85819e5a-02bb-42c8-891f-3ddac485438b) (readonly)&gt;
    &lt;HiddenControl(_formname=migrate_create) (readonly)&gt;&gt;
  </code></pre>
  
  <p>How do i set the value of live or undefinesource (checkbox) to True(ticked) or False(untick)
  Items of live and undefinsource are:</p>
  
  <pre><code>&gt;&gt;&gt; print br.form.controls[4].get_items()
  [&lt;Item name='on' id='migrate_undefinesource' checked='checked' name='undefinesource' type='checkbox' id='migrate_undefinesource' value='on' class='boolean'&gt;]
  &gt;&gt;&gt; print br.form.controls[3].get_items()
  [&lt;Item name='on' id='migrate_live' checked='checked' name='live' type='checkbox' id='migrate_live' value='on' class='boolean'&gt;]
  </code></pre>