simpler synchronization logic with GModel: we now keep track of all internal entities that have been unbound
and we always remove them from GModel

We already did the same thing if a new entity was later re-bound to the tag; but we failed to do it if the *same* entity is rebound.
Since we don't guarantee that the subshapes will stay the same, we need to regenerate the GEntity.

We only delete directly in GModel if nothing was changed in the internal CAD models

- use IsEqual instead of IsSame to check wether we can remove an entity

don't try to preserve tags for fuse (union) operations at the moment: the bahaviour of Modified()/HasModified() is not consistent !?

workaround weird occ bug (?) when hasModified=1 but iterating over all objects/tools does not show anything in Modified()

saw this with a fuse resulting in all entities getting deleted, and a single one created

- if entities are not modified, we keep them as-is
- if an entity gives rise to a single new entity (and we as to delete the intput entity), use the tag of the old entity for the new one

This makes BooleanFragments fully usage for scripted gluing: if shapes are just modified on their boundary they will keep the same tag :-)

This is a major modification of the algorithm: please check carefully!

- the lib example is now the one we use for getdp (with parser & post)