Info-mouse-follow-nearest-node should take prefix arg to fork

[Drew Adams]

Why not add an optional FORK arg to Info-mouse-follow-nearest-node, so it
opens the node in a separate window? The only change is to add the arg and
pass it to Info-try-follow-nearest-node.

(defun Info-mouse-follow-nearest-node (click &optional fork)
    "...
With a prefix argument, open the node in a separate window."
    (interactive "e\nP")
    (mouse-set-point click)
    (and (not (Info-try-follow-nearest-node fork))
         (save-excursion (forward-line 1) (eobp))
         (Info-next-preorder)))