Require user names and emails to be case insensitively unique

Any existing clashes are allowed to remain for now, byt any new
accounts, or changes to names on existing accounts, must be unique
without regard to case.

db/migrate/20111212183945_add_lowercase_user_indexes.rb

@@ -0,0 +1,13 @@
+require 'lib/migrate'
+
+class AddLowercaseUserIndexes < ActiveRecord::Migration
+  def up
+    add_index :users, :display_name, :lowercase => true, :name => "users_display_name_lower_idx"
+    add_index :users, :email, :lowercase => true, :name => "users_email_lower_idx"
+  end
+
+  def down
+    remove_index :users, :name => "users_email_lower_idx"
+    remove_index :users, :name => "users_display_name_lower_idx"
+  end
+end