every commit as it existed in the original repo.  If your repo has 10\^5
files and 10\^5 commits, but each commit only modifies 5 files, then
git-filter-branch will make you do 10\^10 modifications, despite only
having (at most) 5*10^5 unique blobs.</p>
</li>
<li>
<p>If you try and cheat and try to make git-filter-branch only work on
files modified in a commit, then two things happen</p>
<div class="ulist">
<ul>
<li>
<p>you run into problems with deletions whenever the user is simply
trying to rename files 