Free some allocated memory
void SLfree (char *ptr)
The SLfree function uses free to deallocate the memory
specified by ptr, which may be NULL in which case the
function does nothing.
Never use this function to free a hashed string returned by one of
the family of slstring functions, e.g.,
SLang_pop_slstring.
SLmalloc, SLcalloc, SLrealloc, SLmake_string