Change how the "re-open file as root" functionality works

Fixes #850

Use find-file-hook instead of advising ido-find-file.

core/prelude-core.el

@@ -302,13 +302,14 @@ buffer is not visiting a file."
                          (ido-read-file-name "Find file(as root): ")))
     (prelude-find-alternate-file-as-root buffer-file-name)))
 
-(defadvice ido-find-file (after find-file-sudo activate)
+(defun prelude-reopen-as-root ()
   "Find file as root if necessary."
   (unless (or (tramp-tramp-file-p buffer-file-name)
               (equal major-mode 'dired-mode)
               (not (file-exists-p (file-name-directory buffer-file-name)))
               (file-writable-p buffer-file-name))
     (prelude-find-alternate-file-as-root buffer-file-name)))
+(add-hook 'find-file-hook 'prelude-reopen-as-root)
 
 (defun prelude-start-or-switch-to (function buffer-name)
   "Invoke FUNCTION if there is no buffer with BUFFER-NAME.