This is a port of Facebook's [`hg absorb`](https://bitbucket.org/facebook/hg-experimental/src/default/hgext3rd/absorb/__init__.py?at=default&fileviewer=file-view-default), which I first read about on [mozilla.dev.version-control](https://groups.google.com/forum/#!msg/mozilla.dev.version-control/nh4fITFlEMk/ZNXgnAzxAQAJ).

You have a feature branch with a few commits. Your teammate reviewed the branch and pointed out a few bugs. You have fixes for the bugs, but you don't want to shove them all into an opaque commit that says `fixes`, because you believe in atomic commits. Instead of manually finding commit SHAs for `git commit --fixup`, or running a manual interactive rebase, do this:

`git absorb` will automatically identify which commits are safe to modify, and which indexed changes belong to each of those commits. It will then write `fixup!` commits for each of those changes. You can check its output manually if you don't trust it, and then fold the fixups into your feature branch with git's built-in autosquash functionality.