[RFA/JVMTI] Implement DisposeEnvironment

[Tom Tromey]

>>>>> "Keith" == Keith Seitz <keiths@redhat.com> writes:

Keith> [I will be following with several low-hanging-fruit-type patches
Keith> implementing some of the simpler JVTMI functions.]

Unless there is something about one of them that you think is
controversial or tricky or otherwise needing review, I think you can
put these in with just an 'FYI' note.

Tom