[server] add a looping task to free unused cnxsets capture by dead pyro
When a pyro client disconnects, we're not necessarily notified so they
can hang on to their session/cnxset forever. Don't let them do that.
The hacky looping task is only installed when pyro is enabled. This optional
activation save this very hacky patch from being rejected.
closes #2825380
<table class="attributeForm" style="width:100%;"
tal:attributes="id tab_id | nothing;
class tab_class | nothing;">
<tr tal:iter="widget lines">
<th class="labelCol" tal:content="structure python:widget.render_label(entity)">attrname</th>
<td tal:define="error python:widget.render_error(entity)" style="width:100%;"
tal:attributes="class python:error and 'error' or nothing">
<div tal:replace="structure error">error message if any</div>
<div tal:replace="structure python:widget.edit_render(entity)" >widget (input, textarea, etc.)</div>
<div tal:replace="structure python:widget.render_help(entity)">format help if any</div>
</td>
</tr>
</table>