vim: update the patched sh indent file

Signed-off-by: Christopher Larson <kergoth@gmail.com>
vim: switch showbreak character

The previous character could be cut off, depending on the font in use. The new
one is rendered less wide.

Signed-off-by: Christopher Larson <kergoth@gmail.com>
vim: pull undowarnings.vim from damian conway's vim setup

Signed-off-by: Christopher Larson <kergoth@gmail.com>