[web/views/staticcontrollers] Make ConcatFilesHandler write to a tempfile
In order to be more resistant to errors such as ENOSPC, and against different
threads accessing the same static data, we:
- concatenate data files to a temporary file, and rename it once we're done
- delete the tempfile in case of errors
- protect the creation of the cache_concat file with a lock
Closes #3005547
<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>