Add a svn:ignore property to wp-content, wp-content/plugins, and, wp-content/themes to clean up the output of a svn status, this means that plugins/themes/uploads won't clutter the svn status output. Fixes #25337 See #24976


git-svn-id: https://develop.svn.wordpress.org/trunk@25559 602fd350-edb4-49c9-b593-d223f7449a82