Fix NewtCanvasAWT focus traversal for Java7 (Take 2): Commit 70bf3a4ec44504b86294a332255aaae8d2e86bf4 was not sufficient.

Commit 70bf3a4ec44504b86294a332255aaae8d2e86bf4 did not work out on Windows.

Solution now gathers the next or previous 'to be focused' component,
using the FocusTraversalPolicy of the visible/focusable/enabled container.
Then we simply request it's focus.

Works w/ Java7 on Linux and Windows.