remove indexes before renaming tables (some dbs have database-level index namespaces) and unsigned is also a mysqlism

lib/migrate.rb

@@ -49,6 +49,7 @@ module ActiveRecord
         types[:bigint_auto_64] = { :name => "bigint(64) DEFAULT NULL auto_increment" }
         types[:bigint_auto_11] = { :name => "bigint(11) DEFAULT NULL auto_increment" }
         types[:bigint_auto_20] = { :name => "bigint(20) DEFAULT NULL auto_increment" }
+        types[:four_byte_unsigned] = { :name=> "integer unsigned NOT NULL" }
         types
       end