throw '' whenever an interrupt is made (#365, #366)

src/prolog/toplevel.pl

@@ -214,6 +214,9 @@ gather_goals([Var = Value | Pairs], VarList, Goals) :-
     ).
 
 print_exception(E) :-
+    (  E == error('$interrupt_thrown', repl) -> nl % print the exception on a newline to evade "^C".
+    ;  true
+    ),
     write_term('caught: ', [quoted(false), max_depth(20)]),
     writeq(E),
     nl.