Network Admin toolbar menu: Add Plugins and Themes, remove Visit Network.

props Ipstenu, SergeyBiryukov.
fixes #21674.



git-svn-id: http://develop.svn.wordpress.org/trunk@25120 602fd350-edb4-49c9-b593-d223f7449a82
Avoid an undefined index notice when submitting a comment with JavaScript disabled. fixes #24752.

git-svn-id: http://develop.svn.wordpress.org/trunk@25121 602fd350-edb4-49c9-b593-d223f7449a82