As mentionned in the INSTALL files, the default OpenColorIO
configuration files must be downloaded and unpacked at the root of the
Natron source tree, using something like:

    curl -k -L https://github.com/NatronGitHub/OpenColorIO-Configs/archive/Natron-v2.4.tar.gz | tar zxf -
    mv OpenColorIO-Configs-Natron-v2.4 OpenColorIO-Configs
