On Windows, I found that `overrides` contains "PATH+MAVEN" and "Path", and a change by "PATH+MAVEN" was overridden with "Path".
`EnvVars#overrideAll` now handles variables without '+' first, and then handles variables with '+'.

This seems conflict with b95f2694529d22523701e8fe20f4f20b2f4d9fc4.
I could not get what that commit does neither the root cause of [JENKINS-19926] (https://issues.jenkins-ci.org/browse/JENKINS-19926) ...