Handle the -batch option centrally in cmdline.c.

This removes one case from several of the individual tools'
command-line parsers, and moves it into a central place where it will
automatically be supported by any tool containing console.c.

In order to make that not cause a link failure, there's now a
stubs/no-console.c which GUI clients of cmdline.c must include.

unix/plink.c

@@ -735,8 +735,6 @@ int main(int argc, char **argv)
             --argc, ++argv;
         } else if (ret == 1) {
             continue;
-        } else if (!strcmp(p, "-batch")) {
-            console_batch_mode = true;
         } else if (!strcmp(p, "-s")) {
             /* Save status to write to conf later. */
             use_subsystem = true;