[Freeciv-Dev] (PR#4543) scaling overview map

["Erik Johansson" <admerik@xxxxxxxxxxxx>]

> (1) At 1x1, the overview is _very_ small. 

In other games this is done by letting the user choose the
scale/clipping, so I press 'm' (in total war) to change the zoom of the
overviewmap. letting this change dynamically in game is a VERY good thing. 


Suggestions for future patchers:
* clipping might be a good idea, you usually don't need to se all of the
biggest map.
* popup window so you get a zoom which is not abound by the GTK vertical
split. that is like a modalwindow overlapping the playmap. (see pathetic
ascii  graphics under)

.----+---------------------.
|    |                     |
|----+-----.               |
|          |   playmap     |
|  mini    |               |
|  map     |               |
|  zoom 2x |               |
|          |               |
|-----+----'               |
|     |                    |
| left|                    | 
| bar |                    |
|     |                    |
'-----'--------------------'