Tabs: additional check against base href attribute if there is one. Fixed #7822,  - ui.tabs with <base> tag

related to
http://bugs.jqueryui.com/ticket/7822
http://bugs.jqueryui.com/ticket/8637

I tried to comply with the coding standards mentioned here:
https://github.com/jquery/jquery-ui/pull/853

I read a lot of comments on these issues but I still do not know whether you generally do not want to add a feature to make tabs work with BASE-tag or if no-one has come up with something that seemed acceptable to you. If the first case is true, it would be very kind of you to add a short note to the issues or set them to "wontfix" instead.

Thanks.