Dereference pointer when comparing password history in qsort compare.
    
    The man page for qsort(3) says that the comparison function is called
    with pointers to pointers to char but memcmp(3) wants a pointer to void
    so we need to cast and dereference.
    
    Without this the qsort() call wasn't properly sorting the elements so
    a random password was being removed rather than the oldest when the
    list overflowed.
    
    https://fedorahosted.org/freeipa/ticket/2613