Log Message:
Update ruby-actionpack31 to 3.1.8.

## Rails 3.1.8 (Aug 9, 2012)

* There is an XSS vulnerability in the strip_tags helper in Ruby on Rails, the
  helper doesn't correctly handle malformed html.  As a result an attacker can
  execute arbitrary javascript through the use of specially crafted malformed
  html.

  *Marek from Nethemba (www.nethemba.com) & Santiago Pastorino*

* When a "prompt" value is supplied to the `select_tag` helper, the
  "prompt" value is not escaped.
  If untrusted data is not escaped, and is supplied as the prompt value,
  there is a potential for XSS attacks.
  Vulnerable code will look something like this:
    select_tag("name", options, :prompt => UNTRUSTED_INPUT)

  *Santiago Pastorino*