Issue 559: NullPointerException when @NonNull is used in abstract method

- Prevent NPE in javac and give a proper warning in both eclipse and javac
- Add test cases

test/transform/resource/before/NonNullOnParameterAbstract.java

@@ -0,0 +1,7 @@
+abstract class NonNullOnParameterAbstract {
+	public void test(@lombok.NonNull String arg) {
+		System.out.println("Hey");
+	}
+	
+	public abstract void test2(@lombok.NonNull String arg);
+}