Blender Git Loki

Alembic: prevent spaces in names of exported particle systems

Other types already had spaces, periods, and colons replaced by
underscores. The upcoming Alembic exporter (based on the
`AbstractHierarcyIterator` class) will be more consistent and apply the
same naming rules everywhere. This is in preparation for that change.
The `get_?_name()` functions in `abc_util.{cc,h}` will be removed then.