Creating a child item in the same transaction as the parent item gives a PermissionDeniedException

[Nicklas Nordborg]

For example:

Create a scan: scan = Scan.getNew()
Save it: DbControl.saveItem(scan)
Create an image: image = scan.newImage()
Save the image: DbControl.saveItem(image) <<-- PermissionDeniedException

Happens because the permission check in ChildItem class doesn't handle parent items that hasn't been committed to the database yet. A similiar check as in BasicItem.initPermissions needs to be performed in ChildItem.initPermissions

[Nicklas Nordborg]

(In [3073]) Fixes #477: Creating a child item in the same transaction as the parent item gives a PermissionDeniedException