TinyMCE: fix the 'wpgallery' plugin to use a placeholder for galleries when either the 'wpview' plugin or wp.mce is not loaded. Fixes #28756
Built from https://develop.svn.wordpress.org/trunk@29883


git-svn-id: http://core.svn.wordpress.org/trunk@29639 1a063a9b-81f0-0310-95a4-ce76da25c4cd