Secure config errors

If user can make NETHACKOPTIONS point to a file, that user could then
get the file contents via the extended config file error reporting.
Add CONFIG_ERROR_SECURE compile-time option to make that case output
only the first error, no line number or error context.

sys/unix/unixmain.c

@@ -405,7 +405,7 @@ char *argv[];
             }
             break;
         case 'w': /* windowtype */
-            config_error_init(FALSE, "command line");
+            config_error_init(FALSE, "command line", FALSE);
             choose_windows(&argv[0][2]);
             config_error_done();
             break;