What does actually preprocessor directive UNITY5_SCRIPTING_IN_UNITY4 mean?

My guess is that it disallows all the of getter shortcuts that were removed in Unity5. This is in, ummm, 4.62 or above, which came after 5.0 was released?

In Unity5 you have to use the long way, GetComponent<Rigidbody>(), instead of just rigidbody. It’s probably for if you want to make your possible upgrade to Unity5 smoother (in my limited experience, the auto-converter works pretty well, but conversions tend to miss odd cases. This way is better.)