[Freeciv] Windows hidden

[Richard Stallman <rms@xxxxxxx>]

It is very easy to raise the map window accidentally over the messages
window.  If you don't notice that you've done this, the messages
window can remain hidden for many turns.  That is a problem.

One easy way to prevent this is by raising the message window at the
start of each turn, if it is already mapped.  How about it?