gen_visit_union() is now just like gen_visit_struct().  Rename
it to gen_visit_object(), use it for structs, and drop
gen_visit_struct().  Output is unchanged.
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Message-Id: <1453902888-20457-4-git-send-email-armbru@redhat.com>
[split out variant handling, rebase to earlier changes]
Signed-off-by: NEric Blake <eblake@redhat.com>
Message-Id: <1455778109-6278-8-git-send-email-eblake@redhat.com>