Inbound: test parsing RFC2231 MIME header parameters

And decide not to work around a Python 3.3 bug accessing MIME headers
that have non-ASCII characters in params. The bug is fixed in the
Python 3.4 email package (and didn't exist in Python 2.7). Python 3.3
was only supported with Django 1.8.

tests/utils.py

@@ -222,3 +222,20 @@ class ClientWithCsrfChecks(Client):
     def __init__(self, **defaults):
         super(ClientWithCsrfChecks, self).__init__(
             enforce_csrf_checks=True, **defaults)
+
+
+def python_has_broken_mime_param_handling():
+    # In Python 3.3 (only), trying to access any parsed MIME header will crash if the header
+    # has parameters with non-ASCII characters. (Common in, e.g., attachment filenames.)
+    # The bug is somewhere within email._header_value_parser.parse_mime_parameters, and is too
+    # complicated to work around for an uncommon version combination (Django 1.8 on Python 3.3).
+    # If you run into it, please upgrade to (at least) Python 3.4.
+    try:
+        from email.policy import default
+        default.header_fetch_parse("Content-Type", "plain; name*=iso-8859-1''Une%20pi%E8ce")
+    except ImportError:
+        return False  # Python 2 (or pre Python 3.3) -- bug doesn't apply
+    except UnicodeEncodeError:
+        return True  # this is the bug
+    else:
+        return False  # worked fine