* Check NUMKEYS(), similar to f34b61f947
"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).