Ensure header values are native str

PEP 3333 requires that values in the environ that come from
header be native str objects decoded from ISO-8859-1 bytes.
This means that in Python 2 and 3 they are effectively
different things, but oh well, these are the rules.

One area where this causes a real issue is in the
SimpleCookie.load() method which checks for the type of the
string associated with HTTP_COOKIE.

Fixes #39

test/test_wsgi_compliance.py

@@ -50,7 +50,8 @@ def test_more_interesting():
         resp, content = http.request(
             'http://some_hopefully_nonexistant_domain' + expected_uri,
             'GET',
-            headers={'Accept': 'application/json'})
+            headers={'Accept': 'application/json',
+                     'Cookie': 'foo=bar'})
         internal_env = app.get_internals()
 
         expected_path_info = unquote(expected_uri.split('?')[0])
@@ -58,6 +59,8 @@ def test_more_interesting():
         assert internal_env['RAW_URI'] == expected_uri
         assert internal_env['QUERY_STRING'] == 'bar=baz%20zoom'
         assert internal_env['HTTP_ACCEPT'] == 'application/json'
+        assert internal_env['HTTP_COOKIE'] == 'foo=bar'
+        assert type(internal_env['HTTP_COOKIE']) == type('')
 
         # Do the rather painful wsgi encoding dance.
         if sys.version_info[0] > 2:

wsgi_intercept/__init__.py

@@ -220,7 +220,11 @@ def make_environ(inp, host, port, script_name):
 
         k, v = line.strip().split(b':', 1)
         v = v.lstrip()
-        v = v.decode('ISO-8859-1')
+        # Make header value a "native" string. PEP 3333 requires that
+        # string-like things in headers be of type `str`. Much of the
+        # time this isn't a problem but the SimpleCookie library does
+        # type checking against `type("")`.
+        v = str(v.decode('ISO-8859-1'))
 
         #
         # take care of special headers, and for the rest, put them