Syntax error messages

[Hans Åberg]

In order to generate better syntax error messages writing out the input line 
with the error and a line with a marker underneath, I thought of checking how 
Bison does it, but I could not find the place in its sources. —Specifically, a 
suggestion is to tweak YY_INPUT in the lexer to buffer one input line at a 
time, but Bison does not seem to do that.