Log Message:
Update ruby-activerecord to 1.15.2.

Changes:
* Pass a range in :conditions to use the SQL BETWEEN operator. #6974
  [dcmanges] Student.find(:all, :conditions => { :grade => 9..12 })
* Don't create instance writer methods for class attributes. [Rick]
* When dealing with SQLite3, use the table_info pragma helper, so that the
  bindings can do some translation for when sqlite3 breaks incompatibly
  between point releases. [Jamis Buck]
* SQLServer: don't choke on strings containing 'null'.  #7083 [Jakob S]
* Consistently use LOWER() for uniqueness validations (rather than mixing with
  UPPER()) so the database can always use a functional index on the lowercased
  column. #6495 [Si]
* MySQL: SET SQL_AUTO_IS_NULL=0 so 'where id is null' doesn't select the last
  inserted id. #6778 [Jonathan Viney, timc]
* Fixtures use the table name and connection from set_fixture_class. #7330
  [Anthony Eden]
* SQLServer: quote table name in indexes query.  #2928 [keithm@infused.org]