[Freeciv-Dev] (PR#1870) FreecivAC: borders patch

["Jason Short" <jdorje@xxxxxxxxxxxxxxxxxxxxx>]

Another buglet: when drawing in non-iso view, drawing a tile should only
draw within the rectangle of that tile.  For instance, when drawing a
goto line from A=(x,y) to B=(x+1,y) the first half is drawn with tile A
and the second half with tile B.

Otherwise the graphics will be overwritten.  In tile_draw_borders(),
this happens.  See the attached image.  The fix is easy.

This is not an issue in iso view since the overlapping tiles are redrawn
anyway.

jason