bug#27980: disabled-command-function should accept ^G

[積丹尼 Dan Jacobson]

disabled-command-function is an autoloaded compiled Lisp function in
‘novice.el’.

It prompts with

     (message "Type y, n, ! or SPC (the space bar): ")

However in 99% of the cases, the user has triggered it by mistake,
and wishes to get out with ^G, and not be bothered to read the details.

However ^G is disabled here.

Repeated hitting of it will not get one out and back to editing.

I vote ^G be mapped to "n", and be listed in the message.