Jetpack: Bump code to match 3.0.

This changeset encompasses 38 Git commits, summarized here:

https://github.com/Automattic/jetpack/compare/3.0-beta3...3.0



git-svn-id: https://plugins.svn.wordpress.org/jetpack/trunk@918086 b8457f37-d9ea-0310-8a92-e5e31aec5664