Don't lower-case components of background.

Signed-off-by: Edward Z. Yang <ezyang@mit.edu>

tests/HTMLPurifier/URISchemeTest.php

@@ -33,6 +33,12 @@ class HTMLPurifier_URISchemeTest extends HTMLPurifier_URIHarness
         );
     }
 
+    function test_http_uppercase() {
+        $this->assertValidation(
+            'http://example.com/FOO'
+        );
+    }
+
     function test_http_removeDefaultPort() {
         $this->assertValidation(
             'http://example.com:80',