#96 Copy default value into msgline

Many commands have support for default options (isearch, query-replace, zap-/jump-to-char, switch-buffer, shell/open command, etc.) but one thing that is annoying is if you typed the command wrong and hit enter, you have to retype the entire command unless you copy the default with the mouse! Pathetic. I'd like to add a keybinding that yanks the default value into the msgline. Then you can make the editor quick and press enter.

Closed in 7db273a622