merged branch jalliot/header-bag (PR #3702)

Commits
-------

15dd17e Simplified CONTENT_ headers retrieval

Discussion
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Header bag

Bug fix: yes
Feature addition: no
Backwards compatibility break: no
Symfony2 tests pass: yes (actually no but I think this has nothing to do with this PR...)
Fixes the following tickets: -
Todo: -

src/Symfony/Component/HttpFoundation/ServerBag.php

@@ -28,7 +28,7 @@ class ServerBag extends ParameterBag
             }
             // CONTENT_* are not prefixed with HTTP_
             elseif (in_array($key, array('CONTENT_LENGTH', 'CONTENT_MD5', 'CONTENT_TYPE'))) {
-                $headers[$key] = $this->parameters[$key];
+                $headers[$key] = $value;
             }
         }