Problem:    Misspelled mkspellmem as makespellmem.
Solution:   Drop duplicate help entry, fix test. (Naruhiko Nishino, Ken
            Takata, closes vim/vim#4437)
https://github.com/vim/vim/commit/076073950c44ea0e35bc39d539dc7ab41bf9c7ec

Problem:    Using expressions in a modeline is unsafe.
Solution:   Disallow using expressions in a modeline, unless the
            'modelineexpr' option is set.  Update help, add more tests.
https://github.com/vim/vim/commit/110289e78195b6d01e1e6ad26ad450de476d41c1

Problem:    Cannot build without the sandbox.
Solution:   Set the secure option instead of using the sandbox.  Also restrict
            the characters from 'spelllang' that are used for LANG.vim.
            (suggested by Yasuhiro Matsumoto)
https://github.com/vim/vim/commit/82e8c92ebef5afcac0c0fdb706ff163f9b3366f7

closes #9764

The purpose of the {Nvim} hint was not well-defined, and its usage
inconsistent.  It's also unnecessary.

Nvim-Vim differences are centralized at:
    :help vim-differences
Removed things are centralized at:
    :help deprecated
Developer guidelines for documentation are listed at:
    :help dev-doc

- CMake features

Closes #8994

Problem:    Cannot act on edits in the command line.
Solution:   Add the CmdlineChanged autocommand event. (xtal8, closes vim/vim#2603,
            closes vim/vim#2524)

https://github.com/vim/vim/commit/153b704e20f9c269450a7d3ea8cafcf942579ab7

In Vim (and some vestigial parts of Nvim) E319 was a placeholder for
ex_ni commands, i.e. commands that are only available in certain builds
of Vim.  That is obviously counter to Nvim's goals: all Nvim commands
are available on all platforms and build types (the remaining ex_ni
commands are actually just missing providers).

We need an error id for "missing provider", so it makes sense to use
E319 for that purpose.

ref #9344
ref #3577

closes #1466
closes #1007
closes #1391