Bounce all deferreds through the reactor to make debugging easier.

If all deferreds wait a reactor tick before resolving then there is
always a chance to add an errback to the deferred so that stacktraces
get reported, rather than being discarded.

synapse/app/homeserver.py

@@ -33,6 +33,8 @@ if __name__ == '__main__':
         sys.stderr.writelines(message)
         sys.exit(1)
 
+    from synapse.util.debug import debug_deferreds
+    debug_deferreds()
 
 from synapse.storage.engines import create_engine, IncorrectDatabaseSetup
 from synapse.storage import are_all_users_on_domain