synapse claims to require a HEAD request on /_matrix

[richvdh]

https://matrix.org/_matrix says:

Your browser approached me (at /_matrix) with the method "GET".  I only allow the method HEAD here.

... which is a lie. (HEAD gives a 500, per #2029 )

[mldulaney]

Beuler

[mldulaney]

2018-03-22 22:58:30,412 - synapse.storage.TIME - 213 - INFO - - Total database time: 0.001% {_update_client_ips_batch(2): 0.001%, update_user_directory_stream_pos(0): 0.000%, update_cached_last_access_time(0): 0.000%} {}
2018-03-22 22:58:30,434 - twisted - 131 - CRITICAL - - Unhandled Error
Traceback (most recent call last):
File "/usr/lib64/python2.7/site-packages/twisted/protocols/basic.py", line 571, in dataReceived
why = self.lineReceived(line)
File "/usr/lib64/python2.7/site-packages/twisted/web/http.py", line 1752, in lineReceived
self.allContentReceived()
File "/usr/lib64/python2.7/site-packages/twisted/web/http.py", line 1845, in allContentReceived
req.requestReceived(command, path, version)
File "/usr/lib64/python2.7/site-packages/twisted/web/http.py", line 766, in requestReceived
self.process()
--- ---
File "/usr/lib64/python2.7/site-packages/twisted/web/server.py", line 190, in process
self.render(resrc)
File "/usr/lib64/python2.7/site-packages/twisted/web/server.py", line 241, in render
body = resrc.render(self)
File "/usr/lib64/python2.7/site-packages/twisted/web/resource.py", line 250, in render
return m(request)
File "/usr/lib64/python2.7/site-packages/twisted/web/resource.py", line 260, in render_HEAD
return self.render_GET(request)
exceptions.AttributeError: Resource instance has no attribute 'render_GET'