Tests: added tests for a "discard_unsafe_fields" option.

test/python/header_fields/wsgi.py

@@ -0,0 +1,9 @@
+def application(environ, start_response):
+
+    h = (k for k, v in environ.items() if k.startswith('HTTP_'))
+
+    start_response('200', [
+        ('Content-Length', '0'),
+        ('All-Headers', ','.join(h))
+    ])
+    return []