* configuration files for the given @param version of the program.
* If @param version is negative, the build-time string PROGRAM_VERSION
* will be used to determine the version number.
*
* @post user_config_directory() exists IF version was negative.
*
* configuration files for the given @param version of the program.
* If @param version is negative, the build-time string PROGRAM_VERSION
* will be used to determine the version number.
*
* @post user_config_directory() exists IF version was negative.
*