Bug 176882 [DataBinding] Create SWTObservables.observeEditable(...)
We need to provide an observable for the editable property of Text.
tests/org.eclipse.jface.tests.databinding/src/org/eclipse/jface/tests/databinding/swt/SWTObservablesTest.java
assertTrue(value instanceof TextObservableValue);
		assertTrue(text.isListening(SWT.FocusOut));
	}
	public void testObserveTextWithEventOfUnsupportedControl() throws Exception {
		Label label = new Label(shell, SWT.NONE);
		try {
			SWTObservables.observeText(label, SWT.FocusOut);
			fail("Exception should have been thrown");
		} catch (Exception e) {
		}
	}
	public void testObserveTextOfLabel() throws Exception {
		Label label = new Label(shell, SWT.NONE);
		ISWTObservableValue value = SWTObservables.observeText(label);
		assertNotNull(label);
		assertTrue(value instanceof LabelObservableValue);
	}
	public void testObserveTextOfCLabel() throws Exception {
		CLabel label = new CLabel(shell, SWT.NONE);
		ISWTObservableValue value = SWTObservables.observeText(label);
		assertNotNull(label);
		assertTrue(value instanceof CLabelObservableValue);
	}
	public void testObserveTextOfCombo() throws Exception {
		Combo combo = new Combo(shell, SWT.NONE);
		ISWTObservableValue value = SWTObservables.observeText(combo);
		assertNotNull(value);
		assertTrue(value instanceof ComboObservableValue);
		ComboObservableValue comboObservable = (ComboObservableValue) value;
		assertEquals(SWTProperties.TEXT, comboObservable.getAttribute());