[GREENFOOT-711] World can be instantiated even if it cannot be compiled.

If a stale .class file exists the world can be instantiated (via "reset" or opening the scenario) even if the source cannot be compiled. (Also, If it can be compiled - does this mean an out-of-date world potentially gets instantiated?).

Also, editing the world class to introduce an error doesn't appear to mark the class as containing an error - occurs spuriously. Try eg inserting error, if it is marked then remove, reset, re-insert error, etc, several times.

---

Issue metadata

• Issue type: Task
• Priority: Medium