MINOR: http: custom status reason.

The older 'rsprep' directive allows modification of the status reason.

Extend 'http-response set-status' to take an optional string of the new
status reason.

  http-response set-status 418 reason "I'm a coffeepot"

Matching updates in Lua code:
- AppletHTTP.set_status
- HTTP.res_set_status

Signed-off-by: Robin H. Johnson <robbat2@gentoo.org>
diff --git a/include/types/action.h b/include/types/action.h
index 5a70db0..1c17154 100644
--- a/include/types/action.h
+++ b/include/types/action.h
@@ -135,6 +135,7 @@
 		} cap;
 		struct {
 			unsigned int code;     /* HTTP status code */
+			const char *reason;    /* HTTP status reason */
 		} status;
 		struct {
 			struct sample_expr *expr;