list-buffers-noselect needs to lighten up on dedicated windows

[Drew Adams]

emacs -q

(setq special-display-regexps '("[ ]?[*][^*]+[*]"))

M-x list-buffers

*Buffer List* is displayed in its own frame; its window is
window-dedicated-p.

M-x Buffer-menu-revert in *Buffer List* window gives an error: "Window is
dedicated to *Buffer List*".

The attached patch to buff-menu.el fixes the pb (but a more elegant fix can
no doubt be found).

  - Drew

diff-buff-menu-fix.txt
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