ncurses 6.1 - patch 20180414

ncurses 6.1 - patch 20180414

+ modify form library to optionally delay cursor movement on a field
  edge/boundary (patch by Leon Winter).
+ modify form library to avoid unnecessary update of cursor position in
  non-public fields (patch by Leon Winter).
+ remove unused _nc_import_termtype2() function.
+ also add/improve null-pointer checks in other places
+ add a null-pointer check in _nc_parse_entry to handle an error when
  a use-name is invalid syntax (report by Chung-Yi Lin).