Revert "Make the build work with Java 7"

This reverts commit 3110c77199b9189ab094e276ad82f36a6ecef042.

Conflicts:

	pom.xml
	src/main/resources/org/jvnet/hudson/plugins/repositoryconnector/ArtifactResolver/global.jelly
	src/main/resources/org/jvnet/hudson/plugins/repositoryconnector/RepositoryConfiguration/config.jelly
	src/main/resources/org/jvnet/hudson/plugins/repositoryconnector/RepositoryConnector/global.jelly