Install Plugins: Don't wp_die() if API can't be reached.

props johnbillion.
fixes #29361.
Built from https://develop.svn.wordpress.org/trunk@29594


git-svn-id: http://core.svn.wordpress.org/trunk@29368 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Plugins: Only show details link if user can install plugins.

fixes #17902.

Built from https://develop.svn.wordpress.org/trunk@29595


git-svn-id: http://core.svn.wordpress.org/trunk@29369 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Make filter bar CSS less verbose and redundant.

Also removes an unused handler in the theme feature filter.

see #28794.

Built from https://develop.svn.wordpress.org/trunk@29596


git-svn-id: http://core.svn.wordpress.org/trunk@29370 1a063a9b-81f0-0310-95a4-ce76da25c4cd