Log Message:
Update ruby-actionpack31 to 3.1.5.

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

*   Detect optional glob params when adding non-greedy regexp - closes #4817.

*   Strip null bytes from Location header

*   Return the same session data object when setting session id

*   Avoid inspecting the whole route set, closes #1525

*   Strip [nil] from parameters hash.  Thanks to Ben Murphy for reporting this!
    CVE-2012-2660