If you changed the URL segment for your homepage to anything other than 'home'
a new homepage would be created every time you ran a dev/build. This commit
allows you to call RootURLController::set_default_homepage_link('something');
to change the URL segment for your homepage to 'something'. After doing this
the dev/build process will no longer create a homepage if you already have a
page with 'something' as the URL segment.
There was a discussion of needing this at
http://www.silverstripe.org/general-questions/show/12253
