(#2794) - explain normal 404s in console.info

![screenshot 2014-10-05 16 31 19](https://cloud.githubusercontent.com/assets/283842/4519879/bc44853c-4cce-11e4-9883-1e6d8210a463.png)

although TBH web workers are hella broken anyway ATM, and our web worker tests still pass in Chrome with this PR, so...