Add a possibility for plugins to go directly to the WPS after exiting.

It only works for plugins executed via the filebrowser for now. Those
executed from the context menu or a simplelist (such as "Open With...") need additional hacking.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@21680 a1c6a512-1295-4272-9138-f99709370657

apps/plugin.h

@@ -139,6 +139,7 @@ void* plugin_get_buffer(size_t *buffer_size);
 enum plugin_status {
     PLUGIN_OK = 0,
     PLUGIN_USB_CONNECTED,
+    PLUGIN_GOTO_WPS,
     PLUGIN_ERROR = -1,
 };