Include count for \0 character when using strncpy to implement strdup.

We have to include the \0 character in the length when copying a
string with strncpy() for which length was found with strlen().
Otherwise the destination will not get null terminated - except that
we explicitly zeroed it out earlier.

This quiets down the compiler's warnings.

Signed-off-by: Jes Sorensen <jsorensen@fb.com>

dlink.c

@@ -63,7 +63,7 @@ char *dl_strndup(char *s, int l)
     if (s == NULL)
 	return NULL;
     n = dl_newv(char, l+1);
-    strncpy(n, s, l);
+    strncpy(n, s, l+1);
     n[l] = 0;
     return n;
 }