Fix the usage synopsis.
Amend the copyright notice to reflect the fact that there's no Berkeley
code left.
Fix a typo in a comment, improve the descriptions of the way we use
some global variables (relevant to the bug below), and note that
division-by-zero has side effects so the current expression evaluator
can't be trivially extended to arithmetic in its current design.
Avoid hitting an abort(); /* bug */ when in "text mode" (i.e.
ignoring comment state) by updating the line parser state properly.
PR: 53907
eb801906b8