Similar to how you can "!build my-job", the ability to abort that job needs to
be added.

Syntax:

rtyler> !build my-job
hudson> rtyler: job my-job build scheduled now
rtyler> !abort my-job
hudson> rtyler: build of my-job aborted!

If a job wasn't queued or building, the syntax would look like this:

rtyler> !abort my-job
hudson> rtyler: my-job was not building.