Update to 6.2-20200215

While I didn't plan another upgrade, This version incorporate fixes from
kevans@ so let's upgrade to it

Update ncurses to 20200118

Among the changes from before:
- Add support for extended colors on widechar version
- Enable ncurses extended functions
- Enable version 2 of the extended mouse support
-

Update ncurses to 20200118

Among the changes from before:
- Add support for extended colors on widechar version
- Enable ncurses extended functions
- Enable version 2 of the extended mouse support
- Enable SCREEN extensions

Modification that differs from upstream:
- _nc_delink_entries used to be exposed and was turn static,
turn it back as dynamic to not break abi
- Adapt our old termcap.c to modern ncurses

MFC after: 3 weeks

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