- 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!

allow explit/implicit tag assignement in GEO_Internals (same as in OCC_Internals). Implicit is now only for tag < 0 (and not tag <= 0): this is for backward compatibility, because quite a few models define entities "0".

"explicit" OCC_Internals API can now also be used in "implicit" mode (assigning and returning an automatic tag)

We gave the axis [ax, ay, ax] instead of [ax, ay, az]