Tests: HTTP header field and value tests.

test/python/custom_header/wsgi.py

@@ -0,0 +1,7 @@
+def application(environ, start_response):
+
+    start_response('200', [
+        ('Content-Length', '0'),
+        ('Custom-Header', environ.get('HTTP_CUSTOM_HEADER'))
+    ])
+    return []