Autoload a function from a file
int SLang_autoload(char *funct, char *filename)
The SLang_autoload function may be used to associate a
slang function name funct with the file filename
such that if funct has not already been defined when needed,
it will be loaded from filename.
SLang_autoload has no effect if funct has already been
defined. Otherwise it declares funct as a user-defined S-lang
function. It returns 0 upon success, or -1 upon error.
SLang_load_file, SLang_is_defined