Bug 672 (NewtCanvasSWT ignore windowing offset on OSX').

The NewtCanvasSWT is now brought into place by the parent SWT Composite
and the super SWT Canvas it extends. Also added two test cases. One with
a simple SashForm and the NewtCanvasSWT in the second cell, and another
with the NewtCanvasSWT in a Composite, that Composite now in the second
cell of the SashForm. The second test is necessary because the
NewtCanvasSWT does not receive SWT.Resize events in this configuration,
but only SWT.Paint ones (a behaviour inherited from the super SWT
Canvas)