MINOR: http: update the list of cacheable status codes as per RFC7231

Since RFC2616, the following codes were added to the list of codes
cacheable by default : 204, 404, 405, 414, 501. For now this it only
checked by the checkcache option to detect cacheable cookies.

doc/configuration.txt

@@ -5438,8 +5438,9 @@ no option checkcache
   proxy. When this option is enabled, the only responses which can be delivered
   to the client are :
     - all those without "Set-Cookie" header ;
-    - all those with a return code other than 200, 203, 206, 300, 301, 410,
+    - all those with a return code other than 200, 203, 204, 206, 300, 301,
-      provided that the server has not set a "Cache-control: public" header ;
+      404, 405, 410, 414, 501, provided that the server has not set a
+      "Cache-control: public" header field ;
     - all those that result from a request using a method other than GET, HEAD,
       OPTIONS, TRACE, provided that the server has not set a 'Cache-Control:
       public' header field ;

src/proto_http.c

@@ -5388,15 +5388,24 @@ int http_wait_for_response(struct stream *s, struct channel *rep, int an_bit)
 	switch (txn->status) {
 	case 200:
 	case 203:
+	case 204:
 	case 206:
 	case 300:
 	case 301:
+	case 404:
+	case 405:
 	case 410:
-		/* RFC2616 @13.4:
+	case 414:
-		 *   "A response received with a status code of
+	case 501:
-		 *    200, 203, 206, 300, 301 or 410 MAY be stored
+		/* RFC7231#6.1:
-		 *    by a cache (...) unless a cache-control
+		 *   Responses with status codes that are defined as
-		 *    directive prohibits caching."
+		 *   cacheable by default (e.g., 200, 203, 204, 206,
+		 *   300, 301, 404, 405, 410, 414, and 501 in this
+		 *   specification) can be reused by a cache with
+		 *   heuristic expiration unless otherwise indicated
+		 *   by the method definition or explicit cache
+		 *   controls [RFC7234]; all other status codes are
+		 *   not cacheable by default.
 		 *
 		 * RFC7234#4:
 		 *   A cache MUST write through requests with methods