read_term/3 option variable_names/1 doesn't returns pairs in left-to-right traversal order

[pmoura]

The read_term/3 option variable_names/1 doesn't returns pairs in left-to-right traversal order as required by the ISO standard. For details, see e.g.

http://www.complang.tuwien.ac.at/ulrich/iso-prolog/WDCor3

Example to reproduce the compliance bug:

?- current_input(S), read_term(S, T, [variables(L), variable_names(Variables)]).
|: circle(_Id_, _Radius_, _Color_).

L = [_B,_A,_C],
S = user_input,
T = circle(_B,_A,_C),
Variables = ['_Color_'=_C,'_Id_'=_B,'_Radius_'=_A] ? 

yes

It should be:

Variables = [_Id_'=_B,'_Radius_'=_A,'_Color_'=_C,] ? 

This notably breaks Logtalk's parametric object examples.