This is a failed attempt to optimize the usage of the page cache in

This is a failed attempt to optimize the usage of the page cache in
sqlite3BtreeIndexMoveto() by deferring calls to sqlite3PagerUnref() for
child pages of the btree until we are sure those pages will not be reused.
The code does not work in two senses:  (1)  Many tests still fail.
(2) The performance gain is less than 2 million cycles and does not seem
worth the extra risk and complication.

FossilOrigin-Name: 84731a1fd25bd74c8f326a8a8ce3921831eb3d73872564b973bbd81aa406333d