Issue 3631: 2.17 does a worse job with vertical spacing and/or the page layout than...

Issue 3631: 2.17 does a worse job with vertical spacing and/or the page layout than 2.16

Looks for prebroken pieces of dead items in the pure relevant function.

Even if the item is dead, its prebroken pieces may not be.  We need to check
them and build them into the pure skylines of axis groups used by the
align interface.