headers are now properly handled as per the HTTP spec.  As a consequence, if
you had a client that was sending an invalid Content-Type or Accept header to
the API, in 1.2 you will either receive a 415 or 406 error.
The only client
this is known to affect is curl when you use -d with JSON but don't set a
content type, helpfully sends "application/x-www-urlencoded", which is not
correct.