What it is for
The ExternalRedirects-extension allows you to create redirects to pages outside of your mediawiki-installation. External Redirects are essentially broken redirects, so they show up in Special:BrokenRedirects. This patch corrects this behavior.
What it changes
An additional AND-clause is added to the SQL-Statement used to fetch broken redirects.
The HideExternalRedirects-patch for different versions of mediawiki can be found in svn.fsinf.at/mediawiki/patches/SpecialBrokenRedirects.php/.