Workaround #558

Issue #558 is due to interaction between 'after_renaming', human model
having several top-level objects (Human, POS_EMPTY, Human_Camera...) and
a builder script with several human instances.

Instead of solving it properly, this fix simply forbid the user to set the
human name via my_instance.name = my_name Instead, my_name = Human() (ie,
automatic renaming) should be used.

A proper fix involve redesigning the human model to have only a single
top-level object.

See details in the issue #558. Closes #558.