Fix popwin:reuse-window not handle selected frame

popwin.el

@@ -346,10 +346,10 @@ of the value and frame-size."
  :type 'number
  :group 'popwin)
 
-(defcustom popwin:reuse-window 'current-frame
+(defcustom popwin:reuse-window 'current
  "Non-nil means `popwin:display-buffer' will not popup the
 visible buffer. The value is same as a second argument of
-`get-buffer-window'."
+`get-buffer-window', except `current' means the selected frame."
  :group 'popwin)
 
 (defcustom popwin:adjust-other-windows t
@@ -837,6 +837,17 @@ special displaying."
  (popwin:original-pop-to-buffer (car popwin:popup-last-config))
  (error "No popup buffer ever")))
 
+(defun popwin:reuse-window-p (buffer-or-name not-this-window)
+ "Return t if a window showing BUFFER-OR-NAME exists and should
+be used displaying the buffer."
+ (and popwin:reuse-window
+ (let ((window (get-buffer-window buffer-or-name
+ (if (eq popwin:reuse-window 'current)
+ nil
+ popwin:reuse-window))))
+ (and (not (null window))
+ (not (eq window (if not-this-window (selected-window))))))))
+
 (defun* popwin:match-config (buffer)
  (when (stringp buffer) (setq buffer (get-buffer buffer)))
  (loop with name = (buffer-name buffer)
@@ -893,9 +904,7 @@ specifies default values of the config."
 usual. This function can be used as a value of
 `display-buffer-function'."
  (interactive "BDisplay buffer:\n")
- (if (and popwin:reuse-window
- (not (memq (get-buffer-window buffer-or-name popwin:reuse-window)
- (list (if not-this-window (selected-window)) nil))))
+ (if (popwin:reuse-window-p buffer-or-name not-this-window)
  ;; Call `display-buffer' for reuse.
  (popwin:original-display-buffer buffer-or-name not-this-window)
  (popwin:display-buffer-1