Log Message:
Update ruby-activerecord31 to 3.1.5.

## Rails 3.1.5 (May 31, 2012) ##

*   Fix type_to_sql with text and limit on mysql/mysql2. Fix GH #3931.

*   only log an error if there is a logger. fixes #5226

*   fix activerecord query_method regression with offset into Fixnum

*   predicate builder should not recurse for determining where columns.
    Thanks to Ben Murphy for reporting this! CVE-2012-2661