This came up in https://github.com/Homebrew/homebrew-emacs/pull/158#issuecomment-172031003;  `install_metafiles` is passed the current directory, which can be changed during installation by `Dir.chdir`.

There may be cases where the metafiles are in a subdirectory, but my
guess is those are rare and this is brittle and undocumented behavior
anyway.