cubicweb #2174797 config.static_directory content serving is broken [validation pending]

When requesting an existing file in this directory, I get following traceback

Unhandled Error
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/twisted/protocols/basic.py", line 564, in dataReceived
    why = self.lineReceived(line)
  File "/usr/lib/python2.7/dist-packages/twisted/web/http.py", line 1551, in lineReceived
    self.allContentReceived()
  File "/usr/lib/python2.7/dist-packages/twisted/web/http.py", line 1619, in allContentReceived
    req.requestReceived(command, path, version)
  File "/home/florent/Sccp/cubicweb/etwist/server.py", line 482, in requestReceived
    self.process()
--- <exception caught here> ---
  File "/usr/lib/python2.7/dist-packages/twisted/web/server.py", line 126, in process
    resrc = self.site.getResourceFor(self)
  File "/usr/lib/python2.7/dist-packages/twisted/web/server.py", line 542, in getResourceFor
    return resource.getChildForRequest(self.resource, request)
  File "/usr/lib/python2.7/dist-packages/twisted/web/resource.py", line 65, in getChildForRequest
    resource = resource.getChildWithDefault(pathElement, request)
  File "/usr/lib/python2.7/dist-packages/twisted/web/resource.py", line 169, in getChildWithDefault
    return self.getChild(path, request)
  File "/usr/lib/python2.7/dist-packages/twisted/web/static.py", line 315, in getChild
    return self.createSimilarFile(fpath.path)
  File "/usr/lib/python2.7/dist-packages/twisted/web/static.py", line 654, in createSimilarFile
    f = self.__class__(path, self.defaultType, self.ignoredExts, self.registry)
exceptions.TypeError: __init__() takes at most 3 arguments (5 given)
prioritynormal
typebug
done in3.14.7
load0.100
load left0.000
closed by#af813e7d5daa [etwist] fix static directory serving; closes #2174797