Include version as a part of the asset digest

Updates the file digest to take into account the configured version
which allows tasks like invalidating all assets possible again.

Backports rails#404 to 3.x

Author: jacobbednarz

lib/sprockets/loader.rb

@@ -145,7 +145,7 @@ def load_from_unloaded(unloaded)
           source = result.delete(:data)
           metadata = result
           metadata[:charset] = source.encoding.name.downcase unless metadata.key?(:charset)
-          metadata[:digest]  = digest(source)
+          metadata[:digest]  = digest(self.version + source)
           metadata[:length]  = source.bytesize
         else
           dependencies << build_file_digest_uri(unloaded.filename)

test/test_environment.rb

@@ -721,10 +721,10 @@ def setup
     assert_equal 2, asset.metadata[:selector_count]
   end
 
-  test "changing version doesn't affect the assets digest" do
+  test "changing version changes the digest of the asset" do
     old_asset_digest = @env["gallery.js"].hexdigest
     @env.version = 'v2'
-    assert old_asset_digest == @env["gallery.js"].hexdigest
+    assert old_asset_digest != @env["gallery.js"].hexdigest
   end
 
   test "bundled asset is stale if its mtime is updated or deleted" do