Add proxyfix to the dev server as well.

Obviously the dev server shouldn't be used in prod, but when testing
it's helpful for them to behave a little more similarly.

frontends/etiquette_flask/etiquette_flask_dev.py

@@ -2,6 +2,7 @@
 This file is the gevent launcher for local / development use.
 '''
 import gevent.monkey; gevent.monkey.patch_all()
+import werkzeug.middleware.proxy_fix
 
 import argparse
 import gevent.pywsgi
@@ -18,6 +19,7 @@ import etiquette
 import backend
 
 site = backend.site
+site.wsgi_app = werkzeug.middleware.proxy_fix.ProxyFix(site.wsgi_app)
 site.debug = True
 
 HTTPS_DIR = pathclass.Path(__file__).parent.with_child('https')