Add user_id + created_at index to changesets

Browsing changesets for a user will be much faster if we can get the
user's changesets in date order.

db/migrate/20100513171259_add_user_date_index_to_changeset.rb

@@ -0,0 +1,9 @@
+class AddUserDateIndexToChangeset < ActiveRecord::Migration
+  def self.up
+    add_index :changesets, [:user_id, :created_at], :name => "changesets_user_id_created_at_idx"
+  end
+
+  def self.down
+    remove_index :changesets, [:user_id, :created_at], :name => "changesets_user_id_created_at_idx"
+  end
+end