https://github.com/mpeterv/luacheck/pull/81#issuecomment-261099606

> If you really want to use bleeding-edge version you should get the
> rockspec from master branch, not a fixed commit ...
> The correct way to install from a specific commit is cloning that
> commit and running "luarocks make" from project directory. The reason
> is that running "install" or "build" on an scm rockspec fetches
> sources from master but uses build description from the rockspec
> itself, which may be outdated.

`lib/queue.h` implements a basic queue. `event/queue.c` implements
a specialized data structure on top of lib/queue.h; it is not a "normal"
queue.

Rename the specialized multi-level queue implemented in event/queue.c to
"multiqueue", to avoid confusion when reading the code.

Before this change one can eventually notice that "macros (uppercase
symbols) are for the normal queue, lowercase operations are for the
multi-level queue", but that is unnecessary friction for new developers
(or existing developers just visiting this part of the codebase).

- rename to shell_xescape_xquote
- move to os/shell.c
- disallow NULL argument
- eliminate casts, nesting
- test: empty shellxquote/shellxescape

Fixes #2773

Move typedef expand_T to types.h for tests
Fix lint error for old style comments

Describe 'check_ff_value' valid values as an initial test.

Fix 'get_sts_value' comment inaccuracy and add unit test for it

also allow handle==0 meaning curbuf/curwin/curtab

Because the old name did not indicate that the function
would return true on directories as well.