Test if the ignore rules apply to a given path.
This function checks the ignore rules to see if they would apply to the given file. This indicates if the file would be ignored regardless of whether the file is already in the index or committed to the repository.
One way to think of this is if you were to do "git check-ignore --no-index" on the given file, would it be shown or not?
boolean returning 0 if the file is not ignored, 1 if it is
the file to check ignores for, relative to the repo's workdir.
0 if ignore rules could be processed for the file (regardless of whether it exists or not), or an error < 0 if they could not.