[PATCH] support Range and If-Range on send_file and send_data

We can stream multimedia data (videos, audios and so on) by send_file and/or send_data.

In HTML5, we can use and tag to play videos and audios on browser.
Many modern browsers, Firefox, Safari, Google Chrome and so on, support them.

For example, you can see Ogg/Theora video on Firefox at:
http://commons.wikimedia.org/wiki/File:Firefox_3.1b1_pre_(native_Vi...

You will see a control bar which includes play/suspend button, progress bar and volume control at the bottom of video player.

The current Firefox Ogg/Theora video player implementation requires HTTP "Range" supported HTTP server to display total length at the right of progress bar. If a HTTP server doesn't support "Range", progress bar doesn't work. It always indicates the end.
NOTE: Movie can be played correctly even if progress bar doesn't show correct progress.

In Rails, we use send_file and/or send_data to stream movies and/or audios but Rails doesn't support "Range". So we can't play a movie streamed by Rails with correct progress.

Here is a sample Rails application:

% ruby .../edge-rails/railties/bin/rails sample
% cd sample
% ln -fs .../edge-rails vendor/rails
% script/generate controller Streaming index
% vim app/controllers/streaming_controller.rb
app/controllers/streaming_controller.rb:
  class StreamingController < ApplicationController
    def index
      send_file(Rails.root.join("sample.ogv"), :layout => false, :type => "video/ogg")
    end
  end
% wget -O sample.ogv 'http://upload.wikimedia.org/wikipedia/commons/7/79/Firefox_3.1b1_pre_%28native_Videounterst%C3%BCtzung%29.ogg'
% script/server &
% vim /tmp/video.html
/tmp/video.html:
  <html>
    <body>
      <video src="http://localhost:3000/streaming/" controls="true" />
    </body>
 </html>
% firefox /tmp/video.html

You play the movie and then you will notice that progress bar is always filled and total length just indicates played time.

The attached patch supports HTTP "Range" and "If-Range". You will get correct progress with patched Rails.