#2533 autochecklist.nas does not support <group>ing of checklists

[Bea Wolf]

The Aircraft/Generic/autochecklist.nas works only when the <checklist> items are directly in /sim/checklists/, but not when they are grouped using the <group> element. The supplied patch fixes this, even though only when assuming that only the first <group> contains checklists that should be automatically executed, to extend this, a new tag <group-index> or similar could be added for each <index> tag inside /sim/checklists/[startup/shutdown/...].</index></group-index></group></group></checklist>