bug#10144: 24.0.91; `pop-up-frames' with dedicated windows is broken: `C-x C-f'

[Drew Adams]

> According to the Elisp manual `find-file' ... doesn't use
> the selected window if it's strongly dedicated to its buffer.
> So we should either change the manual or revert the change

I see; thanks.  This is definitely a regression from all previous Emacs releases
I'm aware of.  A simpler recipe to reproduce it:

emacs -Q
C-x d some-dir
M-x set-variable pop-up-frames t
(set-window-dedicated-p (selected-window) t)
RET ; on some file name

In Emacs 24 you get the error "Cannot switch...".
In previous releases the chosen file is visited in another frame.

Dedicated windows should be primarily about making Emacs use a different
window/frame.  They should not just prevent showing the file altogether, by
raising an error.