dev-java/concurrent-util needs to be removed from DEPEND/RDEPEND as this has been in the JDK since 1.5. Probably should update the virtual jdk/jre DEP to 1.6. This package also needs to be updated, current is 2.0 that requires Java 6+, February 19 2015|Version: 2.0-beta-1
Dealt with a while ago.