Add InitializePlugin and CleanupPlugin events

We add two events to allow plugins to initialize and cleanup.

EVENTS.txt

@@ -1,3 +1,8 @@
+InitializePlugin: a chance to initialize a plugin in a complete
+		  environment
+
+CleanupPlugin: a chance to cleanup a plugin at the end of a program
+
 StartPrimaryNav: Showing the primary nav menu
 - $action: the current action
 

index.php

@@ -85,3 +85,8 @@ if (!file_exists($actionfile)) {
         $sac->showPage();
     }
 }
+
+// XXX: cleanup exit() calls or add an exit handler so
+// this always gets called
+
+Event::handle('CleanupPlugin');

lib/common.php

@@ -212,3 +212,7 @@ function __autoload($class)
         require_once(INSTALLDIR.'/lib/' . strtolower($class) . '.php');
     }
 }
+
+// Give plugins a chance to initialize in a fully-prepared environment
+
+Event::handle('InitializePlugin');