Fix JSON postback error where the content-type header line can contain more info…

Fix JSON postback error where the content-type header line can contain more info than just the application/json descriptor. Now we just to a compare on the start of the header value.

common/djangoapps/util/json_request.py

@@ -6,7 +6,9 @@ import json
 def expect_json(view_function):
     @wraps(view_function)
     def expect_json_with_cloned_request(request, *args, **kwargs):
-        if request.META['CONTENT_TYPE'] == "application/json":
+        # cdodge: fix postback errors in CMS. The POST 'content-type' header can include additional information
+        # e.g. 'charset', so we can't do a direct string compare
+        if request.META['CONTENT_TYPE'].lower().startswith("application/json"):
             cloned_request = copy.copy(request)
             cloned_request.POST = cloned_request.POST.copy()
             cloned_request.POST.update(json.loads(request.body))