Implement memset_s() and use it instead of zero_bytes().

A new constant, SUDO_CONV_REPL_MAX, is defined by the plugin
API as the max conversation reply length.  This constant can be
used as a max value for memset_s() when clearing passwords
filled in by the conversation function.

src/sudo.h

@@ -75,14 +75,6 @@
 #define MODE_NONINTERACTIVE	0x00800000
 #define MODE_LONG_LIST		0x01000000
 
-/*
- * We used to use the system definition of PASS_MAX or _PASSWD_LEN,
- * but that caused problems with various alternate authentication
- * methods.  So, we just define our own and assume that it is >= the
- * system max.
- */
-#define SUDO_PASS_MAX	256
-
 /*
  * Flags for tgetpass()
  */
@@ -178,9 +170,6 @@ void cleanup(int);
 char *tgetpass(const char *, int, int);
 int tty_present(void);
 
-/* zero_bytes.c */
-void zero_bytes(volatile void *, size_t);
-
 /* exec.c */
 int pipe_nonblock(int fds[2]);
 int sudo_execute(struct command_details *details, struct command_status *cstat);