Switch to libcaca 0.99 beta 19

The old formula referred to
http://caca.zoy.org/files/libcaca/libcaca-0.99.beta18.tar.gz which
cannot be downloaded at the moment. A 0.99 beta 19 was found at
fossies.org and it seems to work. Using beta 19 also obviates the need
for the patch in the current formula.

The only problem I have is that this switches the source of the bottle
from upstream to some third party. Yuck. :-1: 
I contacted the author upstream. We'll see what he or she says.