(math-read-big-expr, math-read-big-bigp): Replace variable lines by

(math-read-big-expr, math-read-big-bigp): Replace variable lines by
math-read-big-lines.
(math-read-big-expr): Replace variables the-baseline, the-h2
and err-msg by math-read-big-baseline, math-read-big-h2 and
math-read-err-msg.
(math-read-big-bigp): Replace variable h2 with math-rb-h2.