Concatenate two strings to produce a hashed string
char *SLang_concat_slstrings (char *a, char *b)
The SLang_concat_slstrings function concatenates two strings,
a and b, and returns the result as a hashed string.
Upon failure, NULL is returned.
A hashed string can only be freed using SLang_free_slstring.
Never use either free or SLfree to free a hashed string,
otherwise memory corruption will result.
SLang_free_slstring, SLang_create_slstring