Improve error reporting.

src/test/res/ids.lua

@@ -0,0 +1,14 @@
+-- utility to give tables and functions uniform ids for testing
+ids = {}
+function id(obj)
+	if not obj or type(obj) == 'number' or type(obj) == 'string' or type(obj) == 'boolean' then
+		return obj
+	end
+	local v = ids[obj]
+	if v then
+		return v
+	end
+	table.insert(ids,obj)
+	ids[obj] = type(obj)..'.'..tostring(#ids)
+	return ids[obj]
+end