check alias/rename to an existing member

Change-Id: Ic0567a6196c213ec3eae9e623344e371a5e69145
improved error marking on missing required methods from interface

Change-Id: I5ec5e05b08ca22729a479a9d15f21b81816a8bdb
check requirements on single interfaces and trait references

This allows to improve error reporting.

Change-Id: If15279f449aa96413d8877167d4351f7cade95c7
moved common code to XtraitjAbstractTest

Change-Id: I34c75e97e27afb25b8fa833d99c6d05fc3b3a181