Log Message:
Update ruby-actionmailer to 1.3.1.

Changes since 1.2.5:
* Make mime version default to 1.0.
* Make sure quoted-printable text is decoded correctly when only portions
  of the text are encoded.
* Make sure DOS newlines in quoted-printable text are normalized to unix
  newlines before unquoting.
* Fixed that iconv decoding should catch InvalidEncoding
* Tighten rescue clauses.
* Automatically included ActionController::UrlWriter, such that URL
  generation can happen within ActionMailer controllers.
* Replace Reloadable with Reloadable::Deprecated.
* Resolve action naming collision.
* ActionMailer::Base documentation rewrite.
* Replace alias method chaining with Module#alias_method_chain.
* Replace Ruby's deprecated append_features in favor of included.