That macro allows to store the time stamp in the `CC_iterator` (the type
of handle for the triangulation vertices and cells), and check that
handle and pointee have the same time stamp.
When a `Vertex` or a `Cell` is recycled by the `Compact_container`,
re-use the existing time stamp instead of increment it. That will avoid
that the pointee of a handle has a changing timestamp.
Previously, each file was using its own implementation of the "compare
handle" function object. This commits adds a new class
`Compare_handles_with_or_without_timestamps` that checks the presence of
`Has_timestamp` in the pointed type, and provides a different
`operator()` depending on that.
Note that, by default, `Triangulation_3::remove` is not deterministic:
it iterates on a `std::map` (or a `boost::unordered_map`) where the key
type is a triple of vertex handles: the order of that iteration depends
on the comparison (or hashing) of pointers.