I am creating a Hudson task that uses the Hudson-defined EXECUTOR_NUMBER
environment variable documented here:

http://wiki.jenkins-ci.org/display/JENKINS/Building+a+software+project#Buildingasoftwareproject-below

When configuring the task, I click on the "Advanced" button under the "Invoking
Ant" section. I then set "Properties" to EXECUTOR_NUMBER=$EXECUTOR_NUMBER.
When Hudson is configured to run N executors (where N > 2), the first two
executors that run have EXECUTOR_NUMBER=1. All subsequent executors have
EXECUTOR_NUMBER=(N-1).

In the documentation, EXECUTOR_NUMBER is said to be unique to for each executor,
however the first two executors always have the same EXECUTOR_NUMBER.