fix crashes when selecting a function category instead of a function
fix crash when deleting a function while test is running

Function::stopAndWait() -> do not test on m_elapsed because its value
can be 0.

Add stopTest() methods in some editors.
Fix the fix: crash when deleting more than one function
fix one last crash when deleting an efxeditor (test not correct)
Merge pull request #258 from plugz/master

Fix crashes in edit mode