fix(md-input): run updateService only..

..if input has no focus. If an input have text and
you delete the text, the label get pulled down into
the input before focus is removed.
This also move an error message downward when using validateTrigger.change.

src/input/input.js

@@ -70,7 +70,9 @@ export class MdInput {
   }
 
   mdValueChanged() {
-    this.updateService.update();
+    if (!$(this.input).is(':focus')) {
+      this.updateService.update();
+    }
     if (this.mdTextArea) {
       $(this.input).trigger('autoresize');
     }