As of your 2006-05-31 `comint.el' change, in both in 21.4 and 21.5
both `shell' and `gdb' commands fail. The message is output:
Invalid function: (macro . #<compiled-function (mode doc &optional init-value
lighter keymap &rest body) "...(660)" [lighter group mode-name keymap mode
body keywordp nil symbol-name easy-mmode-pretty-mode-name t intern "-map"
"-hook" "-on-hook" "-off-hook" :init-value :lighter :global
:extra-args :group :require quote replace-regexp-in-string "-mode\\'"
"" progn defvar format "Non-nil if %s is enabled.
Discarding `comint.el' change is not enough to fix it. Have also to
discard `shell.el' changes.