Setting non-string header values causes Rack errors

As of Rails 2.3, setting a non-string value for a header causes Rack to explode and Apache (in my case) to return 500s at my users.

The test case is simple: create a new app, and a controller something like:

class TestController < ApplicationController
  def pass
    render :text => "ok"
  end   
  def fail
    headers["Expires"] = (Time.now + 10.minutes)
    render :text => "ok"
  end
end

This produces an error like so in Apache's error_log:

[ pid=30425 file=Hooks.cpp:508 time=2009-03-18 16:56:47.412 ]:
  Backend process 30511 did not return a valid HTTP response. It returned: [Content-Length]
*** Exception NoMethodError in application (undefined method 'each' for Wed Mar 18 17:06:47 -0700 2009:Time) (process 30511):
        from /opt/ruby-enterprise-1.8.6-20081215/lib/ruby/gems/1.8/gems/passenger-2.1.1/lib/phusion_passenger/rack/request_handler.rb:73:in 'process_request'

The correct fix to this is likely a fix to Rack, to cast header values to strings, but Rails can patch this by casting values to strings (or enforcing that they be passed as strings) on assignment. I don't have a patch for it at the moment, though, I'm afraid.