apparent race condition when installing a plugin and executing the same plugin in a single build session

Steps to reproduce:

go into <maven>/maven-core-it/it0013

execute:

m2 -cpl -e clean:clean install it0013:it0013

The first time around (if you have a clean local repo WRT it0013), it should simply install the plugin, and run it. HOWEVER, subsequent runs will intermittently result in an NPE in java.util.jar.JarFile. I believe this is a result of initializing the plugin container for it0013:it0013 early in the lifecycle executor in order to determine whether this mojo is an aggregator. When the install mojo completes, it will have overwritten the original artifact file used in this plugin container's classpath. I think this is what's causing the problem, though I can't exactly work out why it's intermittent.

At any rate, we need to address this.