idlwave-shell-expression-overlay. Implemented printing of
expressions on higher levels of the calling stack.
(idlwave-shell-display-level-in-calling-stack): Restore stack
level.
(idlwave-retrieve-expression-from-level): New function.
(idlwave-shell-last-calling-stack): Variable removed.
(idlwave-shell-reset): Argument action reversed (`visible' to
`hidden'). Also remove stop-line overlay.
(idlwave-shell-calling-stack-routine): New variable.
(idlwave-shell-parse-stack-and-display): Messages now display
negative level numbers.
(idlwave-shell-mode): Set `modeline-format'.
(idlwave-shell-display-line): Set `idlwave-shell-mode-line-info'.
(idlwave-shell-make-new-bp-overlay): Fixed glyph display for Emacs
21.
(idlwave-shell-print-expression-function): New option.
