ghci-script-mode: Fix script loading by ghci-script-mode-load.

[Kariiem]

The current version of ghci-script-mode-load is defined as

(defun ghci-script-mode-load ()
  "Load the current script file into the GHCi session."
  (interactive)
  (let ((buffer (haskell-session-interactive-buffer (haskell-session)))
        (filename (buffer-file-name)))
    (save-buffer)
    (with-current-buffer buffer
      (set-marker haskell-interactive-mode-prompt-start (point-max))
      (haskell-interactive-mode-run-expr
       (concat ":script " filename)))))

The let binding calls (haskell-session-interactive-buffer (haskell-session)) which changes the current buffer by calling (haskell-interactive-switch) at haskell-interactive-mode.el::520, this causes the wrong binding for filename and also causes the save-buffer part to prompt for which file to save the *haskell-session* buffer in, which when canceled cancels the rest of the command (haskell-interactive-mode-run-expr (concat ":script " filename)).

[purcell]

Great, thanks.