[Freeciv-Dev] (PR#6205) fix unit popup dialog for gui-gtk

["Jason Short" <jdorje@xxxxxxxxxxxxxxxxxxxxx>]

Now that the unit popup dialog can be given non-owned units (well, it 
always could, but now it's official) some things need to change:

- Better handling of when whe don't know the homecity.  Rather than 
"Musketeers()" we should just have "Musketeers".

- Disable the "Ready all" button if we don't own any units on the tile.

This patch is just for gui-gtk.  Similar changes should be made to other 
clients.

jason