- return result of setting and remove directory if the setting was not
successful.
- don't do `STRCPY` in case of `vim_FullName` failure because
`vim_FullName` already did it.
Though this module is relatively small it has very clear boundaries.
The last argument for extracting `tempfile` was the errors which I got
when I was writing unittests for it: `cimport './src/nvim/fileio.h'`
does not work for some reason.
