Cargo ant target swallows exception details

Trying to run cargo with an invalid config dir throws the exception:

Caused by: org.codehaus.cargo.container.ContainerException: Invalid configuration dir [/Users/CruiseControl/workspace/netstream-build/build/cargo/config]. The configuration dir must point to an empty directory. Note that everything in the configuration dir will get deleted by Cargo.
at org.codehaus.cargo.container.spi.configuration.AbstractStandaloneLocalConfiguration.createConfigurationDir(AbstractStandaloneLocalConfiguration.java:92)
at org.codehaus.cargo.container.tomcat.internal.AbstractCatalinaStandaloneLocalConfiguration.doConfigure(AbstractCatalinaStandaloneLocalConfiguration.java:64)
at org.codehaus.cargo.container.spi.configuration.AbstractLocalConfiguration.configure(AbstractLocalConfiguration.java:157)
... 15 more
org.codehaus.cargo.container.ContainerException: Invalid configuration dir [/Users/CruiseControl/workspace/netstream-build/build/cargo/config]. The configuration dir must point to an empty directory. Note that everything in the configuration dir will get deleted by Cargo.
at org.codehaus.cargo.container.spi.configuration.AbstractStandaloneLocalConfiguration.createConfigurationDir(AbstractStandaloneLocalConfiguration.java:92)
at org.codehaus.cargo.container.tomcat.internal.AbstractCatalinaStandaloneLocalConfiguration.doConfigure(AbstractCatalinaStandaloneLocalConfiguration.java:64)
at org.codehaus.cargo.container.spi.configuration.AbstractLocalConfiguration.configure(AbstractLocalConfiguration.java:157)
at org.codehaus.cargo.container.tomcat.internal.AbstractTomcatInstalledLocalContainer.doStart(AbstractTomcatInstalledLocalContainer.java:74)
at org.codehaus.cargo.container.spi.AbstractInstalledLocalContainer.startInternal(AbstractInstalledLocalContainer.java:225)
at org.codehaus.cargo.container.spi.AbstractLocalContainer.start(AbstractLocalContainer.java:146)
at org.codehaus.cargo.ant.CargoTask.executeActions(CargoTask.java:432)
at org.codehaus.cargo.ant.CargoTask.execute(CargoTask.java:415)

But this detail is dropped in the top level explanation, which says:

BUILD FAILED
/Users/CruiseControl/workspace/netstream-build/build.xml:70: org.codehaus.cargo.container.ContainerException: Failed to start the Tomcat 5.5.16 container. Check the [/Users/CruiseControl/workspace/netstream-build/build/cargo/logs/tomcat-stdout.log] file containing the container logs for more details.

It took a while (and some IM to Vincent) to find this.