Fix reoccurring issue when reading a long input line

[rz137]

The code below works fine but outputs garbage due to M2 breaking the input line (when outputting it back). Don't just break the line by printWidth... Instead, use better sentinels.

--%mode=original
bar = (op1,op2) -> ({op1,op2,op1|op2} / (op->print(degree op, isHomogeneous(op), degrees op)); null)

i1 : mode(false); << "[magic succeeded] mode = original";
[magic succeeded] mode = original
(op), degrees op)); null){op1,op2,op1|op2} / (op->print(degree op, isHomogeneous 

o2 = bar

o2 : FunctionClosure