Store dirty flag in each registry key and use it to save only modified
branches.

server/select.c

diff --git a/server/select.c b/server/select.c
index 24cbdb6..5149013 100644
--- a/server/select.c
+++ b/server/select.c
@@ -225,7 +225,7 @@
 /* SIGTERM handler */
 static void sigterm_handler()
 {
-    close_registry();
+    flush_registry();
     exit(1);
 }