Also:
- rename a spellcheck file to match curl.
- editorconfig: fix line width.
- editorconfig: make it use UTF-8.
- editroconfig: apply some rules to all files.
- .gitignore: drop dupe, drop `.DS_Store` (not created by this repo),
sort.
- .gitignore: add for tests executables.
Closes#1718
This gets us large file support, is available on any VMS release
in the last decade and more, and gives stat other modern features
such as 64-bit ino_t.
