Delete expired IP bans at cron time

Because there is no point in letting the table fill up with records that are excluded from the ip ban queries.

--- Base (BASE)
+++ Locally Modified (Based On LOCAL)
@@ -589,3 +589,12 @@
     'sbl-xbl.spamhaus.org'
   )));
 }
+
+/**
+ * Implementation of hook_cron
+ */
+function troll_cron() {
+
+  // Clean up expired IP addresses from IP ban table
+  db_query('DELETE FROM {troll_ip_ban} WHERE expires > 1000000000 AND expires < %d', time());
+}