Updating "jetpack" submodule/ WP plugin from 2.9.1 to 3.0,

* @georgestephanis, Tue May 20 18:27:56 2014 +0000 "Jetpack: Tag 3.0 release."
* https://github.com/wp-plugins/jetpack/releases/tag/3.0
* Code: https://github.com/wp-plugins/jetpack/commit/acf238965a53daa3
* Tag: https://github.com/wp-plugins/jetpack/commit/91be0d7370000326