Added static helper method to Library interface for getting the wrapp…

…ed NativeLibrary instance.

src/com/sun/jna/Library.java

@@ -271,4 +271,12 @@ public Object invoke(Object proxy, Method method, Object[] inArgs)
             }
         }
     }
+
+    static final NativeLibrary getNativeLibrary(final Library library) {
+        final Class<?> interfaceClass;
+        if (!Library.class.isAssignableFrom(interfaceClass = library.getClass())) {
+            throw new IllegalArgumentException("Interface " + interfaceClass.getSimpleName() + " does not extend " + Library.class.getSimpleName());
+        }
+        return ((Handler)Proxy.getInvocationHandler(library)).getNativeLibrary();
+    }
 }