Fix when reconciliation of large page results in a single, small page.

In the case of a workload where we're forcibly evicting a large page, but most of the page is discarded during reconciliation and the page doesn't split into multiple chunks, we were quitting, leaving the page in place.  Instead, instantiate the page and swap it into place to replace the previous version. Reference #1317.

@michaelcahill, I think this is ready for review.