* Fix sites that use about:blank redirect technique
When you open some links with Google Calendar, instead of opening the link directly, the site opens a new window with the location 'about:blank' and then sets the new window's document content to include a refresh directive to open the actual link. This change causes the 'about:blank' links to be handled internally so that the technique can actually work.
* Hide 'about:blank' windows while they perform the redirect
After a new window is created for an 'about:blank' link, the redirect occurs, which causes another window to be opened. This change causes the 'about:blank' to be created hidden, and then closed entirely once the redirect finishes.
* Add tests for `linkIsInternal`
* Refactor onNewWindow to make it testable
