ExceptionHandler should auto-wrap Grails ValidationException to get human-readable message

[amcclain]

In RestController we catch/wrap Grails GORM ValidationExceptions in our own Hoist version of the same - the Hoist class processes the message into something that's actually readable.

https://github.com/xh/hoist-core/blob/develop/grails-app/controllers/io/xh/hoist/RestController.groovy#L76

Any reason not to always do this within ExceptionHandler so it is the default serialization for that class of exceptions?