Move script_setup() back to immediately before we drop privs and

call the new script_nextid() in its place, which will set
sudo_user.sessid for the logging functions.

sudo.h

@@ -326,6 +326,7 @@ void selinux_exec __P((char *, char *, char **, int));
 void aix_setlimits __P((char *));
 #endif
 int script_execv __P((const char *, char * const *));
+void script_nextid __P((void));
 void script_setup __P((void));
 int term_cbreak __P((int));
 int term_copy __P((int, int));