Introduce our own shutdown callback mechanism.

Instead of adding stuff to `_shutdown()`, we can now register a shutdown
routine from the respective `init()` function of our modules.

This also has the advantage, that we're sure they're called in reverse
order from how the initialization happened.

I didn't simply use `atexit()` because POSIX says that the number of
possible callbacks is limited (min 32) and I was not sure whether
we will maybe extend this number at one point.

Signed-off-by: Steffen Jaeckel <s@jaeckel.eu>

src/config/tlscerts.c

@@ -56,10 +56,25 @@ static Autocomplete certs_ac;
 
 static char* current_fp;
 
+static void
+_tlscerts_close(void)
+{
+    free_keyfile(&tlscerts_prof_keyfile);
+    tlscerts = NULL;
+
+    free(current_fp);
+    current_fp = NULL;
+
+    autocomplete_free(certs_ac);
+}
+
 void
 tlscerts_init(void)
 {
     log_info("Loading TLS certificates");
+
+    prof_add_shutdown_routine(_tlscerts_close);
+
     load_data_keyfile(&tlscerts_prof_keyfile, FILE_TLSCERTS);
     tlscerts = tlscerts_prof_keyfile.keyfile;
 
@@ -356,18 +371,6 @@ tlscerts_free(TLSCertificate* cert)
     }
 }
 
-void
-tlscerts_close(void)
-{
-    free_keyfile(&tlscerts_prof_keyfile);
-    tlscerts = NULL;
-
-    free(current_fp);
-    current_fp = NULL;
-
-    autocomplete_free(certs_ac);
-}
-
 static void
 _save_tlscerts(void)
 {