As described in tech-userlevel:
- Modify the writing code to only write entries in the new
format for the terminal descriptions that require it.
- Store new format entries as <name>@v3
- Store old format entries with clamped values as <name> for
backwards compatibility
- Lookup first <name>@v3 and then <name> if that is not found.
- Don't create terminfo2 anymore; old programs keep working with
clamped entries, and new programs be able to use the wide
fields with using the original db file.

terminfo: promote numeric parameters from short to int

POSIX mandates implementations must support upto a short but may exceed it.
When NetBSD terminfo was implemented, no terminfo description used over
a short, but because ncurses has supported ints for some time, some now do.

Infact, such a terminfo description was imported where colour pairs for
screen-256color went up to 65536 which exposed a bug in the existing
implementation where it set to zero. Because the number might mean
something more than a range, we need to be able to store it accurately.

This requires a version bump because whilst the API hasn't changed thanks
to C int promotion, the ABI has. Also the underlying database structure
has changed as well - we now store the numeric paramter inside a uint32_t
field rather than a uint16_t one.
Whilst this change can still read the old style database, the old one
cannot read the new one and thus we now maintain the database as
terminfo2.cdb, leaving the old library and database alone so old programs
still work fine.

libcurses, libfrom, libmenu and libpanel have also been bumped to
accomoate this change.

Switch terminfo(3) to cdb(5).

branches: 1.2.6; 1.2.8;
Retain commented out capabilities by default.

Import my terminfo implementation.
This uses the ncurses terminal definitions.

OK: core@, jdc@