Jetpack: branching trunk into a dev branch.

 * Trunk will now be used to carry all "release-anytime" fixes and updates, and be used for major and minor releases.
 * Dev branch will now be used for features meant to go live during major releases only, having potential to "break things" in the meantime.

On major releases:
 * sync dev branch to trunk, 
 * tag release from trunk

On minor releases:
 * tag release from trunk



git-svn-id: http://plugins.svn.wordpress.org/jetpack/branches/dev@573627 b8457f37-d9ea-0310-8a92-e5e31aec5664