Rethrow ActionController::UnknownAction exceptions encountered by

the API so that rails handles them in the normal way and shows
the 404 page to the user. Closes #1989.

app/controllers/application_controller.rb

@@ -192,6 +192,8 @@ class ApplicationController < ActionController::Base
       report_error message, :bad_request
     rescue OSM::APIError => ex
       report_error ex.message, ex.status
+    rescue ActionController::UnknownAction => ex
+      raise
     rescue Exception => ex
       logger.info("API threw unexpected #{ex.class} exception: #{ex.message}")
       ex.backtrace.each { |l| logger.info(l) }