Workaround for IE dropping the leading slash in pathnames

Various versions of Internet Explorer seems to neglect the leading slash under some conditions (not when watching it with the dev tools of course!). This was confirmed in IE10 + IE11

Fixes #809.
Then we really are left without any workaround. Documentation on the subject is basically non-existent... the closest thing I can find is http://devdocs.io/dom/urlutils, which seems to suggest that there should always be a leading slash.