Browser Unpack Example Does Not Work

``` sh
$ browserify x.js y.js > bundle.js
$ browser-unpack < bundle.js | factor-bundle \
x.js -o bundle/x.js \
y.js -o bundle/y.js \
> bundle/common.js
```

`bundle/common.js` is created. Neither `bundle/x.js` or `bundle/y.js` are created. It is my understanding that these bundles should be created with the modules that exist in the common bundle being omitted.
- browserify@11.0.1
- factor-bundle@2.5.0
- browser-unpack@1.1.1

Reproduce the shell commands with browserify@11.0.1, factor-bundle@2.5.0, and browser-unpack@1.1.1. Trace how factor-bundle handles the browser-unpack output, then verify that bundle/x.js and bundle/y.js are created with modules shared in bundle/common.js omitted.

Written by the indexing model from the issue text.