better error message on index fail

main.go

@@ -60,7 +60,7 @@ func handleUpload(w http.ResponseWriter, r *http.Request) {
 
 	err = updateIndex()
 	if err != nil {
-		httpError(w, r, "Could not update index", http.StatusInternalServerError)
+		httpFail(w, r, "Could not update index", err)
 		// best-effort to remove the file if we could not update the index
 		os.Remove(p)
 		return