Bug 65276 [Preferences] Preference dialog should disable OK when okPressed
bundles/org.eclipse.jface/src/org/eclipse/jface/preference/PreferenceDialog.java
final Sash sash = new Sash(composite, SWT.VERTICAL);
		sash.setLayoutData(new GridData(GridData.FILL_VERTICAL));
		
		
		sash.addListener(SWT.Selection, new Listener() {
			/*
			 * (non-Javadoc)
			 * 
			 * @see org.eclipse.swt.widgets.Listener#handleEvent(org.eclipse.swt.widgets.Event)
			 */
			public void handleEvent(Event event) {
				if (event.detail == SWT.DRAG)
					return;
				int shift = event.x - sash.getBounds().x;
				GridData data = (GridData) treeControl.getLayoutData();
				int newWidthHint = data.widthHint + shift;
				if (newWidthHint < 20)
					return;
				Point computedSize = getShell().computeSize(SWT.DEFAULT,
						SWT.DEFAULT);
				Point currentSize = getShell().getSize();
				
				
				boolean customSize = !computedSize.equals(currentSize);
				data.widthHint = newWidthHint;
				setLastTreeWidth(newWidthHint);
				composite.layout(true);
				
				computedSize = getShell().computeSize(SWT.DEFAULT, SWT.DEFAULT);