"dumb" Unix terminals are not supported

[murarth]

A "dumb" terminal is any Unix terminal that does not provide a terminfo entry, such as those implemented by gvim and emacs. These terminals do not provide the operations expected by linefeed and therefore, linefeed must implement some workaround when running within one of these terminals. GNU Readline uses simple cursor movement, space, and backspace to support all draw operations in "dumb" terminals.