automatically removing missing files beneath a directory

["Geoffrey Irving" <irving@naml.us>]

If I have a subdirectory in a git repository, and I remove some files
without telling git, is there is a simple way to automatically run the
equivalent of 'git rm' for all the missing files?  git commit -a would
work, except that I only want to remove files beneath a particular
subdirectory.  git add <directory> does the equivalent operation for
adding files, but I don't see a way to automatically remove them
without parsing the output of git status.

Thanks,
Geoffrey