Option to restrict layer to a single tileset

Cocos2d only allows one tileset per tile layer. It is very easy to accidentally click the tile stamp tool on the wrong layer and it can be difficult to undo the problem if it is not noticed immediately. What is worse, Cocos2d can not recover from this problem and completely fails to load the tileset.

I would like to request a checkbox option in preferences to enforce "one tileset per layer". After a given tileset has been used in a layer, then an error dialog will appear if the end user tries to use a different tileset with that layer.

No files or tests are mentioned. Start by locating the preferences UI and the tile stamp tool handling, then trace how a layer records its tileset and how errors are shown. Done means an optional preference prevents applying a different tileset to a layer and displays an error dialog without breaking tileset loading.

Written by the indexing model from the issue text.