correct rake test:prepare so it seeds the db correctly

move category creation into seeds as well, so db can be seeded from structure.sql

lib/tasks/db.rake

@@ -2,3 +2,7 @@
 task 'db:migrate' => 'environment' do
   SeedFu.seed
 end
+
+task 'test:prepare' => 'environment' do
+  SeedFu.seed
+end