Request: Properly shown diamond boundaries for isometric maps

[ghost]

Isometric maps currently seem to enforce a diamond shaped editable area. However, tiled shows a rectangular area that is larger than that and has uneditable areas outside of the map borders shown aswell.

Those areas aren't highlighted in any way, and even when moving the mouse on top of them, no indication is given (different mouse cursor or anything) that the tile which the mouse points at isn't in the editable range. Only as soon as one clicks, it actually becomes obvious that this tile cannot be edited.

There should be a clear visual indication (preferrably a thin line or something around the editable area) that shows the map boundaries to make it easier for mappers to keep them in mind when editing.

[bjorn]

Closing this as a duplicate of issue #10, which is about the same problem.

For now you can enable the grid to see the boundaries, but I agree there should be something indicating the boundaries also when the grid is off.