[Fix #15] Fix Java 7 compatibility issue

For now, all the newly added Java 7 methods are implemented by throwing
an UnsupportedOperationException. This allows us to keep Java 6
compatibility.

See also 6b10b62ad77edcd3491d972179f0a47e08002982 which we should use
once we abandon Java 6.
Merge pull request #20 from agouge/15-2

[Fix #15] Fix Java 7 compatibility issue