The Internet Engineering Task Force approved the new HTTP status code 451.…

The Internet Engineering Task Force approved the new HTTP status code 451. Adding to status.py and docs appropriately.

docs/api-guide/status-codes.md

@@ -89,6 +89,7 @@ The 4xx class of status code is intended for cases in which the client seems to
     HTTP_428_PRECONDITION_REQUIRED
     HTTP_429_TOO_MANY_REQUESTS
     HTTP_431_REQUEST_HEADER_FIELDS_TOO_LARGE
+	HTTP_451_UNAVAILABLE_FOR_LEGAL_REASONS
 
 ## Server Error - 5xx
 

rest_framework/status.py

@@ -65,6 +65,7 @@ HTTP_417_EXPECTATION_FAILED = 417
 HTTP_428_PRECONDITION_REQUIRED = 428
 HTTP_429_TOO_MANY_REQUESTS = 429
 HTTP_431_REQUEST_HEADER_FIELDS_TOO_LARGE = 431
+HTTP_451_UNAVAILABLE_FOR_LEGAL_REASONS = 451
 HTTP_500_INTERNAL_SERVER_ERROR = 500
 HTTP_501_NOT_IMPLEMENTED = 501
 HTTP_502_BAD_GATEWAY = 502