sldb-show-source and slime-highlight-sexp need longer timer for slime-flash-region

[mon_key]

When source buffer is not displaying on a visible window, `sldb-show-source' is
not able to `slime-highlight-sexp' because `slime-flash-region' does not delay
long enough for the window to be raised.

Following patch modifies `slime-highlight-sexp' by adding a new local variable
`flash-delay` which checks if the source buffer's window is window-live-p and
adjusts to run-with-timer for a longer period if not.

(defun slime-highlight-sexp (&optional start end)
  "Highlight the first sexp after point."
  (let ((start (or start (point)))
 (end (or end (save-excursion (ignore-errors (forward-sexp)) (point))))
        (flash-delay
         (if (window-live-p (get-buffer-window (current-buffer))) 0.2 0.4)))
    (slime-flash-region start end flash-delay)))