Support java 7

This PR includes all my contributions about the support of java 7 (for now, only test cases because spoon supports a lot of things about this version of java).

Some questions must to be discuss in the community. These questions are explained in these issues: https://github.com/INRIA/spoon/issues/96 and https://github.com/INRIA/spoon/issues/97.
Could you remove this import ?