THINGS TO DO

(These should be resolved before releasing the next version.)

Fix 1-degree-interval meridian drawing in nw-europe.

Fix wind speed/acp calcs for voyages.

Fix usage of update_cell_display bitmask in mac interface.

Fix dragging behavior of scrollbar thumbs.

Fix drawing of centered maps in tk interface.

Fix behavior of protection table.

Fix when acp < 0 and acp-min < 0 so that multiple move-to actions
during turn will work.

In Mac interface, fix drawing offset mistakes when x-scrolling at 8x8.
