$ brew update
error: Your local changes to the following files would be overwritten by merge:
    httpd24.rb
Please, commit your changes or stash them before you can merge.
Aborting
Error: Failed to update tap: homebrew/apache
Already up-to-date.

$ git status
On branch master
Untracked files:
  (use "git add <file>..." to include in what will be committed)

    Library/Formula/httpd24.rb

nothing added to commit but untracked files present (use "git add" to track)

cd $(brew --repository)
git reset --hard FETCH_HEAD

git --git-dir $(brew --repository)/.git reset origin/master --hard
git --git-dir $(brew --repository)/.git clean -fd