add @SuppressWarnings("unused")

because @SuppressWarnings("PointlessBooleanExpression") is not understood by
Eclipse. This does eliminate 64 warnings in the eclipse IDE.
I do not remove the @SuppressWarnings("PointlessBooleanExpression"), because I cannot test, whether other IDE's (IDEA?) will be happy with only SuppressWarnings("unused")

(sorry, I have to reapply this change, because I did remove this feature with PR #274 yesterday. I did the wrong solution to get PR#274 clean ...)