- Also remove feature-detection of uv_set_vterm_state(): instead, on
  Windows we always require libuv to have that function.

Problem:    Needlessly searching for tilde in string.
Solution:   Only check the first character. (James McCoy, closes vim/vim#3734)
https://github.com/vim/vim/commit/ef0a1d5ed3566b91143d30ae9de3240f47c6e282

FreeBSD console sets TERM=xterm, but it does not support xterm features
like cursor-shaping. GUI terminals typically set TERM=xterm-256color, so
on FreeBSD we can guess that TERM=xterm is the degraded vt.

OpenBSD console sets TERM=vt220
https://github.com/openbsd/src/blob/master/etc/etc.amd64/ttys

NetBSD console sets TERM=vt100
https://github.com/NetBSD/src/blob/trunk/etc/etc.amd64/ttys

closes #8644

The macOS preferences have a section called `Language & Region`. There is always
at least one language defined, the primary language.

CFLocaleCopyPreferredLanguages() returns the languages defined in that section,
the first element being the primary language.

Use the primary language in case CFLocaleCopyCurrent() returns NULL.

In the case that the above fallback does not work either, which is very
unlikely, log the error and continue with an empty $LANG.

References #9134

* os/fs.c: add os_isdir_executable()
* eval.c: fix hang on job start caused by non-executable cwd option
* channel.c: assert cwd is an executable directory
* test: jobstart() produces error when using non-executable cwd

ref https://github.com/neovim/neovim/issues/9001#issuecomment-421843790

Steps to reproduce:
    :set verbose=9
    :call system(['echo'])
    E730: using List as a String