Eliminated colons and added single quotes to list of valid choices in menu error message.
Reimplemented Menu#update_responses and Question#build_responses to move all logic to the latter.
Fixed comment.
Restored use of message_source.inspect for nonstrings.  Fixed tests to not expect colons.
Merge pull request #101 from keithrbennett/clarifies_menu_error_message

Eliminated colons and added single quotes to list of valid menu choices