ought putty-256color use xterm-256color rather than 256setaf?

[Nick Black]

I was debugging a user's bug report regarding PuTTY 0.74 on
Debian Unstable [0]. The TERM environment variable was defined
to "putty-256color". Under this configuration, `ccc` is not
exported, despite PuTTY seemingly supporting `ccc` (both by
claim and by my testing).

This seems due to putty-256color inheriting from xterm+256setaf,
which does not support initc/ccc. I assumed this was an error,
but consulting the release notes suggests that this was done
purposefully 2014-03-30 in a patch by Sven Zühlsdorf. I traced
this to a 2014-03-26 mail to bug-ncurses@:

  https://lists.gnu.org/archive/html/bug-ncurses/2014-03/msg00019.html

I'm unsure whether PuTTY did indeed lack support for ccc in 2014
(no version number is reported in the mail) [1], but my testing
seems to confirm that it does support it now. Might it be
reasonable to subclass from "xterm-256color" or some other
database entry?

Actually, I just found [2], which suggests that Mr. Dickey is
aware of PuTTY's ability to change the palette in response
to Linux console-style palette controls. So perhaps I'm just
missing something regarding terminfo internals? My apologies if
this bug report is invalid.

--rigorously, nick

[0] https://github.com/dankamongmen/notcurses/issues/1295
[1] Thomas Dickey's response on
    
https://stackoverflow.com/questions/47686906/ncurses-init-color-has-no-effect
    would seem to suggest that PuTTY lacked initc/ccc support
    as late as 2017-12-07
[2] 
https://stackoverflow.com/questions/64867745/how-to-dynamically-change-text-color-in-a-linux-terminal-using-putty
    Quite recent, 2020-11-17.

-- 
nick black -=- https://www.nick-black.com
to make an apple pie from scratch,
you need first invent a universe.

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