Currently host does not use a version, which means it's not protected
against race conditions of either itself or its value objects. This adds
and plumbs through version to ensure that if a host or its value objects
change that they are not going to be affected by a race condition.
This adds a parameter to host sets allowing the sync interval to be
user-specified on a per-host-set basis. A value of -1 disables syncing;
a value of null uses the current default.
Todd
Jeff Mitchell