** -- malloc'ed memory. Then free "s1".
*/
char *
-add(char *s2, char *s1)
+add(const char *s2, char *s1)
{
char *cp;
size_t len1 = 0, len2 = 0;
** string of length 0.
*/
char *
-mh_xstrdup(char * s)
+mh_xstrdup(const char * s)
{
char * tmp;
tmp = strdup(s ? s : "");