Stop marshalling any.Any types unnecessarily.

Fixes #576.

runtime/errors.go

@@ -95,17 +95,7 @@ func DefaultHTTPError(ctx context.Context, mux *ServeMux, marshaler Marshaler, w
 	body := &errorBody{
 		Error: s.Message(),
 		Code:  int32(s.Code()),
-	}
-
-	for _, detail := range s.Details() {
-		if det, ok := detail.(proto.Message); ok {
-			a, err := ptypes.MarshalAny(det)
-			if err != nil {
-				grpclog.Printf("Failed to marshal any: %v", err)
-			} else {
-				body.Details = append(body.Details, a)
-			}
-		}
+		Details: s.Proto().GetDetails(),
 	}
 
 	buf, merr := marshaler.Marshal(body)