Fixes XSS vulnerability in the translate helper method

@NZKoz @lest,

I'm working on a patch for https://groups.google.com/forum/?fromgroups=#!topic/rubyonrails-security/K2HXD7c8fMU.

I based it off of the 3.0 patch, however, I'm not quite sure how to deal with the `keys` as an Array. So I've aired on the safer side and chosen to make all options html-safe.

What do you think?