when the op was a "user modify" (a non-watch write), and the durable
user_version is updated according to the following rules:
1) set user_at_version to the maximum of ctx->new_obs.oi.user_version+1
- and info.last_user_version+1.
+and info.last_user_version+1.
2) set user_at_version to the maximum of itself and
- ctx->at_version.version.
+ctx->at_version.version.
3) ctx->new_obs.oi.user_version = ctx->user_at_version (to change the
- object's user_version)
+object's user_version)
This set of update semantics mean that for traditional pools the
user_version will be equal to the past reassert_version, while for