New development build, with new toys.
* Major internal refactoring/cleanup of keyboard input. Keyboard input
processing might now be marginally faster on slow machines.
* Cleanup - make all yes/no prompts have the same, consistent format.
* Move message command (copy messages+expunge from the original folder).
* Setup screen - use an external editor to compose new messages.
* Setup screen - confirm before quitting Cone.
* Additional color terminal support. Colors of various elements on the
folder listing screen can now be set from the setup screen.