Handling errors for 'Too Many Requests' and 'Identical Record' conditions

Basecamp currently allow 500 requests per 10 second (from the same IP address for the same account), and if your app exceeds this limits, it sends an error with error_code 429. 

Also, Basecamp keeps track of changes in last 5 mins and if exactly same content is sent to Basecamp within this time, it sends an error with error_code 422.

I found these two necessary for error handling, so I am suggesting this change for everyone else too :)