Don't show welcome panel when it's been dismissed on the same major version. Ignore minor version differences.

git-svn-id: https://plugins.svn.wordpress.org/contact-form-7/trunk@860586 b8457f37-d9ea-0310-8a92-e5e31aec5664
Ready for 3.7.1 release.

git-svn-id: https://plugins.svn.wordpress.org/contact-form-7/trunk@860653 b8457f37-d9ea-0310-8a92-e5e31aec5664