[e4-dev] New Sash handling

[Eric Moffatt <emoffatt@xxxxxxxxxx>]

I've just committed a version of the
'non composite' based sash layout mechanism described in bug 317849.

This is a significant change and I fear
it may well affect some of the other components (XWT, Tom's tooling)...

The main change in the model is that
the result of rendering an MPSC is a 'widget' that is actually an SWT Rectangle
(its 'bounds' in the old widget). 

So far everything looks fine to me barring
a single layout issue when un-splitting stacks. 

It's main new feature is that you can
place the cursor at the intersection of multiple sashes and drag both at
once...

The real feature is that it's actually
being model based...the layout works directly against the UI Model's elements,
leading to much stabler code due to no synchronization issues between the
model and SWT's SashForm. This means that no matter how complex a sub-structure
of sashes you have the widget hierarchy will be only two widgets deep,
the widget using the new "SashLayout" and its leaf widgets (at
whatever level they are in the sash structure). This should lead to much
smoother layout characteristics...

Eric