Libcaca input/output driver

[samhocevar]

The attached patch adds support for libcaca: http://zoy.org/~sam/patches/0002-First-go-at-a-libcaca-input-output-driver.patch

The patch causes libcaca to take precedence over ncurses if the CACA macro is defined. I am not familiar with SCons so I do not know how to autodetect the library. But libcaca uses standard pkg-config on Linux systems, so it should be pretty easy to do.

Everything could be improved a lot, but I first wanted to know whether there was interest in that feature.

I only tested it on Linux, but I believe this adds text mode support on Windows.

[samhocevar]

I put a screenshot at http://people.zoy.org/~sam/caca-df.png