We need `volatile' option to properly update matched candidates.
Faster matching.
Performance fix: checking untracked files costs too much.
- Use '-uno' option to exclude untracked files on an update check for
  modified files
- Skip update check for untracked files since 'git status' costs as the
  same as 'git ls-files --others --exclude-standard'
Pass `default-directory' by `anything-attrset'.
Asynchronously retrieve file list.