flag warning if any outer has same name as feature

[michaellilltokiwa]

I think it is almost always a bad idea to name a feature same as one of its outers. We might want to show a warning if this is the case.

[fridis]

Right, using an outer feature's name for an inner feature is probably not a good idea. However, we get similar problems when inheriting features that happen to have the same name as an outer feature. What is important to me is to cause an error whenever there is an ambiguity, so any unqualified use of a feature f that exists at different outer levels should cause an error. As for warnings: we do have some warnings, but generally, something should either be allowed or forbidden, there should be little in-between.