Publishing aliases of unpublished pages

[magnetised]

Publishing a page that contains a piece that's an alias to an unpublished page causes problems as the piece's target will be nil.

Piece aliases that point to unpublished pages should exclude themselves from the publishing scope -- i.e. act like they're invisible.

Page aliases that are being published should declare a dependency on the target page in the publishing dialogue.

Page aliases that point to unpublished pieces should declare a dependency on the page that owns the target piece.