One of the tests remains disabled until we figure out the expected
behaviour of mkdir() on Windows when `prot` is passed.

Closes #5759

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 itself, which may be outdated.

In order to not conflict with new error codes that Vim adds, all Neovim
error codes should be above 5000.  The three existing sub-5000 error
codes (E926, E951, and E952) are now E50003, E5004, and E5005
respectively.

E953 was removed in 6167ce6df2753d5474ad49aea19f5957128ab015, so just
remove it from the help.

Change shada reencoding tests to check for
correct handling of UTF-8 and binary strings.

Delete enc=latin1 json tests.

The 'dump and read back mark " from a closed tab' test needs to actually
create a second tab.  Since it wasn't doing so, the 'q!' command caused
nvim to exit and the subsequent 'qall' command fails.

Problem:    Mark " is not set when closing a window in another tab. (Guraga)
Solution:   Check all tabs for the window to be valid. (based on patch by
            Hirohito Higashi, closes vim/vim#974)

https://github.com/vim/vim/commit/e59215c7dcae17b03daf39517560cfaa03314f5a

Before this change,

    nvim -i /etc/shada

segfaults on exit if the file does not exist and user does not have
permissions to create the file at /etc/shada.

Closes #5296
Reported in #5277
https://github.com/neovim/neovim/issues/5277#issuecomment-243937255