ruby 2.1.0: get rid of all references to Curses

colorpair.rb, sup.rb and keymap.rb all have references to curses and the internal wrappers of ruby. They seem to be gone in 2.1.0 on my installation, anyway, we shouldn't need them.

https://www.ruby-lang.org/en/news/2013/12/25/ruby-2-1-0-is-released/
https://bugs.ruby-lang.org/issues/8584
https://github.com/shugo/curses
https://github.com/ruby/curses