The messages on this output are exactly the strings associated with the target name in the introduction to the target.
can eat its own dog food"
Gant can build and install used to be used for building and installing itself and is being used for various build tasks including building Groovy and Java programs, static websites, LaTeX documents, not to mention being an integral part of Grails. The ability to have arbitrary Groovy methods within the build scripts makes a Gant build script so much easier to work with that the mix of XML and Groovy scripts that using Ant necessitates. But then maybe this is an issue of individual perception. But then Gant is not about replacing Ant, it is about having a different way of working with the tasks and infrastructure that Ant provides.
Gant isn't really a "build framework"
Gant is just a lightweight façade on Groovy's AntBuilder. It just a way of scripting Ant tasks using Groovy. Gant can be used to do do build tasks (see above about "eating its own dog food"), but it doesn't have the integrated artefact dependency management, project lifecycle management, and multi-module/sub-project support that a fully fledged build framework should provide. Gradle on the other hand is a complete build framework based on Groovy and Ivy. If you just want to do some Ant task scripting then Gant is probably the tool you need, but for replacing Ant and Maven as build frameworks (so as to get rid of all the XML and use Groovy), then you probably need to consider Gradle.
And yes, Gant is managed by a Gradle build of Gant is under development to replace the Ant (and Gant!) builds.
It is probably worth noting that Gradle grew out of work done on Gant.