Bug 118429 [DataBinding] Validation should use IStatus, not just Strings
In order to use data binding in Workbench or IDE dialogs and preference pages, we need validation in terms of IStatus objects. Using strings is too simplistic. For example, look at the wizard for creating a new class. You will get a warning if the class name does not start with an uppercase letter, or if you don't provide a package name, but you will still be able to click "Finish" to proceed anyway. (Note that IStatus is currently not on the classpath, we need to re-introduce the dependency on org.eclipse.equinox.common, which contains IStatus etc.)
bundles/org.eclipse.core.databinding/src/org/eclipse/core/internal/databinding/ValueBinding.java
if (modelToTargetConverter == null) {
				throw new BindingException(
						"Missing model to target converter from " + model.getValueType() + " to " + target.getValueType()); 
			}
			if (!context.isAssignableFromTo(model.getValueType(),
					modelToTargetConverter.getFromType())) {
				throw new BindingException(
						"model to target converter does not convert from model type. Expected: " + model.getValueType() + ", actual: " + modelToTargetConverter.getFromType()); 
			}
			if (!context.isAssignableFromTo(modelToTargetConverter.getToType(),
					target.getValueType())) {
				throw new BindingException(
						"model to target converter does convert to target type. Expected: " + target.getValueType() + ", actual: " + modelToTargetConverter.getToType()); 
			}
			model.addValueChangeListener(modelChangeListener);
		}
		if (bindSpec.isUpdateModel()) {
			targetToModelConverter = bindSpec.getTargetToModelConverter();
			if (targetToModelConverter == null) {
				throw new BindingException(
						"Missing target to model converter from " + target.getValueType() + " to " + model.getValueType()); 
			}
			if (!context.isAssignableFromTo(target.getValueType(),
					targetToModelConverter.getFromType())) {
				throw new BindingException(
						"target to model converter does not convert from target type. Expected: " + target.getValueType() + ", actual: " + targetToModelConverter.getFromType()); 
			}
			if (!context.isAssignableFromTo(targetToModelConverter.getToType(),
					model.getValueType())) {
				throw new BindingException(