LeibnizGraph<T>::operator>>(): call set_jacobiator_and_leibniz_targets()
LeibnizGraph<T>::operator>>(): call set_jacobiator_and_leibniz_targets()

This hadn't yet lead to problems since copies of LeibnizGraphs were made
in LeibnizGraph<T>::map_from_istream(), and this function was called
on the copies when they were constructed.

rburing/kontsevich_graph_series-cpp