WT_REF arrays have to be processed when the page is discarded: we can't
using the "index" array, because for internal splits that deepend the
tree, and for the single "split" page that disappears during split into
a parent, the "index" array won't reference all of the possible WT_REF
elements.   For now: copy WT_REF key/addresses in all cases, so they can
be individually freed, and walk the lists of WT_REFs, not the index array.
We also have to free the WT_REFs originally created for the page.