ncurses: vendor import version 6.5

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
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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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Import ncurses 5.6-20071222 snapshot onto the vender branch

Import ncurses 5.6-20061217 onto the vender branch

Approved by: delphij

Import ncurses-5.2-20010512 onto the vendor branch

Obtained from: ftp://dickey.his.com/ncurses/