In some cases, some partial resync roots would be missed during the
partial resync process, leading to incomplete resync of all the needed
data.
This was caused by tagging some liboverrides for resync _after_ they had
already be evaluated as part of parenting hierarchy of other
liboverrides. Fix is simply to split both steps apart, such that all IDs
that need it are tagged to resync first, and then hierarchies are
evaluated to find the required partial resync roots whithin a hierarchy.
9ea2170cce