FEATURE: add clean support for running Discourse in a subfolder

To setup set DISCOURSE_RELATIVE_URL_ROOT to the folder you wish

lib/middleware/turbo_dev.rb

@@ -17,11 +17,12 @@ module Middleware
     end
 
     def call(env)
-      is_asset = (env['REQUEST_PATH'] =~ /^\/assets\//)
+      root = "#{GlobalSetting.relative_url_root}/assets/"
+      is_asset = env['REQUEST_PATH'] && env['REQUEST_PATH'].starts_with?(root)
 
       # hack to bypass all middleware if serving assets, a lot faster 4.5 seconds -> 1.5 seconds
       if (etag = env['HTTP_IF_NONE_MATCH']) && is_asset
-        name = $'
+        name = env['REQUEST_PATH'][(root.length)..-1]
         etag = etag.gsub "\"", ""
         asset = Rails.application.assets.find_asset(name)
         if asset && asset.digest == etag