add special handeling of too long path's

[JoC0de]

fixes #688

[igor84]

Still can hit the problem but I guess it reduced a chance for it a bit.

[JoC0de]

@igor84 The only problem I see is that it will not produce consistent results on different machines when someone places the same Unity project in a "longer" path and gets e.g. the issue that a DLL is not found beaus it doesn't have the same name. To really solve the inconsistency we would need a setting that forces the path shortening. Eventually we can make the whole Path shortening optional so the user knows that it happens but probably the potential issues will occur when the user forgot that he enabled it. But I think all of this is relay an edge case.