[Haml] Fix #capture under Rails 3.

Closes gh-174

doc-src/HAML_CHANGELOG.md

@@ -3,6 +3,11 @@
 * Table of contents
 {:toc}
 
+## 3.0.5 (Unreleased)
+
+* Make sure the `#capture` helper in Rails 3
+  doesn't print its value directly to the template.
+
 ## 3.0.4
 
 [Tagged on GitHub](http://github.com/nex3/haml/commit/3.0.4).

lib/haml/helpers/action_view_mods.rb

@@ -85,7 +85,9 @@ module ActionView
       module CaptureHelper
         def capture_with_haml(*args, &block)
           if Haml::Helpers.block_is_haml?(block)
-            capture_haml(*args, &block)
+            str = capture_haml(*args, &block)
+            return ActionView::NonConcattingString.new(str) if defined?(ActionView::NonConcattingString)
+            return str
           else
             capture_without_haml(*args, &block)
           end