travis-ci/travis-core — pull request #266 by drogus (2013-10-14 12:08:45+00:00)
Title: Send amqp messages to workers after canceling the build.

From commit message:

```
When a build was cancelled we were not sending cancel messages to
workers, which means that while the job was set into canceled state, a
worker was still busy running the build.
```

This is the fix for travis-ci/travis-ci#1507