Some permission fixes

'view' is checked against Header objects too.
We currently have no moderation for those, so this wasn't called,
but it should really be more general than just PostRevision ;)

Also pretty sure that all users can see log excerpts for hidden/deleted
stuff, at least that's how it works in other parts of MW (deletion
log is accessible to all)

Change-Id: I62413fc89422d8d98842e0f2b03ab0bdc093c343
Merge "Some permission fixes"