vim: update vim-suda and supporting framework

vim: update vim-suda and supporting framework

- vim-suda was updated to remove `setlocal backup`, so the rc no longer handles
  that option. (#85)
- didn't notice at the time but even if undofile is set during :read or enabled
  after, the buffer's undo stack is not updated, so expand the undofile save to
  also read the undofile when loading suda:// buffers.