Otherwise terrain textures cache has zero hits because it stores not normalized
paths. Due to implicit conversion it's possible to add entry with
addEntryToObjectCache passing a string that is converted into normalized path.
But then getRefFromObjectCache called with original value does not find this
entry because it's not converted and overloaded operators are used instead.
We can take elsid's commit 605cb8d further by avoiding the terrain sync completely in most cases. Currently in changeCellGrid we wait for a new preloading task to ensure the getPagedRefnums for the new active cells have been filled in by object paging. This is usually not necessary because we have already completed a preload in the past containing these active cells. With this PR we remember what we preloaded and skip the terrain sync if it is not needed.
