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
aae38d10b4