Fixed: sudo plugin interfering with vim-mode + cursor position #3141

This patch alters the sudo-plugin's bindkey for sudo-command-line, which is eating up the `ESC` key used on vim-mode to enter command mode.

The *bug* only affects people using vim-mode; the *fix* changes the bindkey to `C-_`. 

Guess this needs design In lieu of inter-compatibility between the two modes.

incorporates #3141
replaces #2522