Fix BytesWarning with -bb in wsgiref.headers.Headers.
diff --git a/Lib/test/test_wsgiref.py b/Lib/test/test_wsgiref.py
index cea3565..cfadfbd 100755
--- a/Lib/test/test_wsgiref.py
+++ b/Lib/test/test_wsgiref.py
@@ -426,15 +426,20 @@
 
         h[b"Foo"] = bytes(b"bar")
         self.assertEqual("bar", h.get("Foo"))
+        self.assertEqual("bar", h.get(b"Foo"))
 
         h.setdefault(b"Bar", b"foo")
         self.assertEqual("foo", h.get("Bar"))
+        self.assertEqual("foo", h.get(b"Bar"))
 
         h.add_header(b'content-disposition', b'attachment',
             filename=b'bud.gif')
         self.assertEqual('attachment; filename="bud.gif"',
             h.get("content-disposition"))
 
+        del h['content-disposition']
+        self.assert_(b'content-disposition' not in h)
+
 
 class ErrorHandler(BaseCGIHandler):
     """Simple handler subclass for testing BaseHandler"""