Hallvard Furuseth authored Sep 10, 2017 and Quanah Gibson-Mount committed Feb 11, 2018

* Check NUMKEYS(), similar to f34b61f9
  "ITS#8722 fix FIRST_DUP/LAST_DUP cursor bounds check".
* Move XCURSOR_INITED() into XCURSOR_REFRESH().  This adds a check in
  mdb_cursor_put, below /* converted, write the original data first */.
* Factor mc_ki[] out to XCURSOR_REFRESH().
* Replace an mc_pg[] with mp which is equal (mdb_cursor_del0).