conf2: bugfix in editing and adding before/after a node of a link list

conf2: bugfix in editing and adding before/after a node of a link list

interpret_add_list() allocates memory himself, hence it is not suitable for
these operations.  since the real code is only 2 lines long, I moved the
functionality to closing_brace().  I changed its interface too, hence it
can be used much simpler and interpret_line() can be returned to its
original form.