export LEX-ERROR and modify it to carry entire LEXSTATE.

[NicholasBHubbard]

I needed access to the LEX-ERROR condition but it was not exported so I exported it along with its readers. I cannot see any reason why this would be a problem.

While I was at it I thought that LEX-ERROR should have a slot that holds the entire LEXSTATE instead of just the LINE and SOURCE. By having access to the LEXSTATE I can create more meaningful error messages for the user. Note that I exported LEXSTATE's readers as well.

Let me know what you think.