title: jqGrid formatter and sortable column - doesn't sort
body: <p>I am using a custom formatter for my jqGrid columnModel and I can't get sorting to work with formatter functions.  If I remove formatter column sorts normally.</p>
  
  <pre><code>jQuery("#listAgentOptions").jqGrid({
      height: 240,
      datatype: "local",
      colNames: [' ', 'First Name', 'Last Name', 'Role'],
      colModel: [
      { name: 'status', index: 'status', width: 18, sorttype: 'text', align: 'center', formatter: function(cellvalue, options, rowObject) {
          return cellvalue == 1 ? "&lt;img src='images/agent_green_s.png' alt='Ready' title='Ready' /&gt;" :
          cellvalue == 3 ? "&lt;img src='images/agent_red_s.png' alt='Busy' title='Busy' /&gt;" :
          "&lt;img src='images/agent_orange_s.png' alt='Pending Ready' title='Pending Ready' /&gt;";
      },
          unformat:
      function(cellvalue, options, rowObject) { return Math.floor(Math.random() + 0.1).toString(); }
      },
      { name: 'firstName', index: 'firstName', width: 92 },
      { name: 'lastName', index: 'lastName', width: 142 },
      { name: 'role', index: 'role', sorttype: 'int', width: 36, align: 'center', formatter: function(cellvalue, options, rowObject) {
          return cellvalue == true ? "&lt;img src='images/user_gray.png' alt='Supervisor' title='Supervisor' /&gt;" : "&lt;img src='images/user.png' alt='Agent' title='Agent' /&gt;";
      }, unformat:
      function(cellvalue, options, rowObject) { return cellvalue; }
      }
      ],
      sortname: 'lastName'
  });
  </code></pre>
  
  <p>Rows are added like this:</p>
  
  <pre><code>jQuery("#listAgentOptions").jqGrid('clearGridData');
  $.each(result, function(i, item) {
      if (item.ContactType == 1) {
          jQuery("#listAgentOptions").jqGrid('addRowData', i+1, { firstName: item.ContactName.split(" ")[0], lastName: item.ContactName.split(" ")[1],
          role: item.IsSupervisor,
          status: item.Status == "Ready" ? 1 : item.Status == "Busy" ? 3 : 2
          });
      }
  });
  </code></pre>
  
  <p>How do I get sorting to work properly?</p>
  
  <p><strong>Update.</strong> I have just downloaded the latest version of jqGrid - same issue.</p>
  
  <p>I have also tried using <code>unformat: function(cellvalue, options, rowObject) { }</code> but cellvalue is empty there :-E When I use <code>return Math.floor(Math.random() + 0.1).toString();</code> it does sort things randomly (each time I click), but <code>return cellvalue;</code> just returns an empty string.</p>