When wrapping Java exceptions, their toString() methods are called from the wrapper's Error() method to satisfy the Go error interface. Make sure toString() is always included, even if it never directly referenced from bound packages. Change-Id: I5653f6ad82afbe4b061e02a69d60453000288a83 Reviewed-on: https://go-review.googlesource.com/35189 Reviewed-by: David Crawshaw <crawshaw@golang.org>