Replace insecure tmpfile() with mkstemp() based local tempfile()

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

helpers.h

@@ -69,6 +69,8 @@ int     makepath        (char *path);
 void    ifconfig        (char *ifname, char *addr, char *mask, int up);
 
 int     atonum          (char *str);
+FILE   *tempfile        (void);
+
 void    runlevel_set    (int pre, int now);
 int     runlevel_get    (void);
 char   *runlevel_string (int levels);