Make the multi-get calls throw 400 errors on invalid input

Also refactor ways and relations to use the same structure as nodes

app/controllers/way_controller.rb

@@ -84,23 +84,23 @@ class WayController < ApplicationController
   end
 
   def ways
-    begin
-      ids = params['ways'].split(',').collect { |w| w.to_i }
-    rescue
-      ids = []
+    if not params['ways']
+      raise OSM::APIBadUserInput.new("The parameter ways is required, and must be of the form ways=id[,id[,id...]]")
     end
 
-    if ids.length > 0
-      doc = OSM::API.new.get_xml_doc
+    ids = params['ways'].split(',').collect { |w| w.to_i }
 
-      Way.find(ids).each do |way|
-        doc.root << way.to_xml_node
-      end
-
-      render :text => doc.to_s, :content_type => "text/xml"
-    else
-      render :text => "", :status => :bad_request
+    if ids.length == 0
+      raise OSM::APIBadUserInput.new("No ways were given to search for")
     end
+
+    doc = OSM::API.new.get_xml_doc
+
+    Way.find(ids).each do |way|
+      doc.root << way.to_xml_node
+    end
+
+    render :text => doc.to_s, :content_type => "text/xml"
   end
 
   ##