Changes to nested assets not reflected in parent asset checksum

Checksums of files that reference other assets should take into account the names of those nested assets after they've been revisioned.

A simple example of when this surfaces is anytime you have a file such as a CSS file, referencing another file such as a background image, and the background image is changed but not renamed.
In this instance, the CSS file checksum remains the same, even though it correctly points to the new background image checksum.

I don't actively use broccoli so I can't offer much insight beyond this bug report, but I figured it might help given that those of us who actually care about fingerprinting are also the ones affected by such issues :) Hope this helps.