path.js needs to handle absolute url paths

[ebidel]

Absolute urls are handled incorrectly. If a component contains:

<link rel="components" href="/static/libs/toolkit/src/g-component.html">

urlToPath() resolves the url to:

http://localhost/static/webcomponents/demos/components/my-components//static/libs/toolkit/src/g-component.html

So the xhr fails.

Note: the URL should be http://localhost/static/libs/toolkit/src/g-component.html