Silent failure when trying to require missing file

[dgtombs]

Steps to reproduce:

1. Try to require a file that does not exist, e.g., //= require ./doesnotexist.js

Expected Result:

Asset-pipeline fails the build or at least outputs a warning about the missing file.

Actual Result with asset-pipeline v2.9.1:

There is no warning. The requirement is silently dropped.

[thojo]

Should optionally be possible so that missing files would be noticed immediately.

[stefanrother]

Definitely. I'd like to put this as a step into our Continuous Delivery Pipeline.