Refine fade-out animation of floating validation tips. 1) Don't hide them, instead just make transparent and move to lower layer. 2) Don't fade out them when just mouse-over on its input field.

git-svn-id: https://plugins.svn.wordpress.org/contact-form-7/trunk@839443 b8457f37-d9ea-0310-8a92-e5e31aec5664