Update jquery.form.js to 3.51.0-2014.06.20.

git-svn-id: https://plugins.svn.wordpress.org/contact-form-7/trunk@941288 b8457f37-d9ea-0310-8a92-e5e31aec5664
Update POT

git-svn-id: https://plugins.svn.wordpress.org/contact-form-7/trunk@941291 b8457f37-d9ea-0310-8a92-e5e31aec5664