Allow linkless items in the admin bar. Improve non-jQuery admin bar tabbing....

Allow linkless items in the admin bar. Improve non-jQuery admin bar tabbing. fixes #19277, #19149, #19164, #15519. see #18197, #19088.

git-svn-id: https://core.svn.wordpress.org/trunk@19328 1a063a9b-81f0-0310-95a4-ce76da25c4cd