Add David Underhill's git-purge-from-history script from his blog

Author: unixorn

README.md

@@ -110,6 +110,7 @@ git clone this repository, then add it to your `$PATH`. Nothing here actually re
 * git-outgoing - Michael Markert's [dotfiles](https://github.com/cofi/dotfiles)
 * git-promote - Trevor's [Improving My git Workflow](http://hoth.entp.com/2008/11/10/improving-my-git-workflow) blog post
 * git-publish - Michael Markert's [dotfiles](https://github.com/cofi/dotfiles)
+* git-purge-from-history - David Underhill’s [blog](http://dound.com/2009/04/git-forever-remove-files-or-folders-from-history/)
 * git-rank-contributors - William Morgan <wmorgan-git-wt-add@masanjin.net>
 * git-rebase-authors - Mislav Marohnić's [dotfiles](https://github.com/mislav/dotfiles)
 * git-rel - Ryan Tomayko's [dotfiles](http://github.com/rtomayko/dotfiles)

git-purge-from-history

@@ -0,0 +1,27 @@
+#!/bin/bash
+set -o errexit
+ 
+# Author: David Underhill
+# Script to permanently delete files/folders from your git repository.  To use 
+# it, cd to your repository's root and then run the script with a list of paths
+# you want to delete, e.g., git-delete-history path1 path2
+#
+#  retrieved from: http://dound.com/2009/04/git-forever-remove-files-or-folders-from-history/
+#
+ 
+if [ $# -eq 0 ]; then
+    exit 0are still
+fi
+ 
+# make sure we're at the root of git repo
+if [ ! -d .git ]; then
+    echo "Error: must run this script from the root of a git repository"
+    exit 1
+fi
+ 
+# remove all paths passed as arguments from the history of the repo
+files=$@
+git filter-branch --index-filter "git rm -rf --cached --ignore-unmatch $files" HEAD
+ 
+# remove the temporary history git-filter-branch otherwise leaves behind for a long time
+rm -rf .git/refs/original/ && git reflog expire --all &&  git gc --aggressive --prune