^A/#repeat vs extended commands

Fix '#repeat' for tty; both it and ^A can repeat an extended command.

Fix both for curses; they can repeat an extended command instead of
just repeating the initial '#' to start getting an extended command.

X11 (tested), Qt (tested), and probably Windows GUI (not tested)
behave the same as before:  ^A (or #repeat) after an extended command
just repeats the # to run the dialog to get an extended command.

I hope this introduces fewer bugs than it fixes but I don't think I'd
bet on that....

win/X11/winmisc.c

@@ -1556,8 +1556,13 @@ X11_get_ext_cmd(void)
     /* The callbacks will enable the event loop exit. */
     (void) x_event(EXIT_ON_EXIT);
 
-    if (extended_cmd_selected < 0)
+    if (extended_cmd_selected < 0) {
+        if (!g.in_doagain)
+            savech(0);
         return -1;
+    }
+    if (!g.in_doagain)
+        savech_extcmd(command_list[extended_cmd_selected], TRUE);
     return command_indx[extended_cmd_selected];
 }