Cleanup radio widget's MSG_CURSOR

[mooffie]

While investigating #3719 I discovered a "bug" in the radio widget:

Whenever a key is pressed (MSG_KEY), the widget draws itself to reflect the new state. But instead of doing this drawing explicitly, it does this indirectly by focusing the widget in its MSG_CURSOR. This is a vestige from the old days.

I'm attaching a bug to fix this.

Why is this a problem? Because:

1. MSG_CURSOR has one defined purpose. It shouldn't be piggybacked for other things. This causes trouble:

2. One way to fix #3719 is simply by adding "case MSG_FOCUS: r->pos = r->sel". This resets the active item to the selected one whenever the user moves the focus to the widget. But since MSG_FOCUS is outrageously sent in MSG_CURSOR also, this reset will be done after each key press, which means that the active item is stuck...

[mooffie]

Another issue (independent of the above):

We should also replace the widget_set_state(WST_FOCUSED) with widget_redraw(), in case MSG_KEY: case ' ' (the patch at #3718 makes it send a proper notification). We may put a widget_set_state(WST_FOCUSED) in MSG_HOTKEY instead. (I'm not attaching a patch b/c I won't have time to check it right now.)

[andrew_b]

Branch: 3721_radio_msg_cursor
changeset:6c47fa36d3b28d7795b2f00ab15a2e9fb46d92f5

[andrew_b]

Merged to master: [effac4744974ab6327070330236fada475d7c723].