add hooks for upgrades

EVENTS.txt

@@ -1418,3 +1418,7 @@ StartShowInvitationSuccess: Right before showing invitations success msg
 EndShowInvitationSuccess: After showing invitations success msg
 - $action: invitation action
 
+StartUpgrade: when starting a site upgrade
+
+EndUpgrade: when ending a site upgrade; good place to do your own upgrades
+

scripts/upgrade.php

@@ -33,6 +33,7 @@ require_once INSTALLDIR.'/scripts/commandline.inc';
 
 function main()
 {
+    if (Event::handle('StartUpgrade')) {
         updateSchemaCore();
         updateSchemaPlugins();
 
@@ -50,6 +51,9 @@ function main()
         initFaveURI();
         initSubscriptionURI();
         initGroupMemberURI();
+
+        Event::handle('EndUpgrade');
+    }
 }
 
 function tableDefs()