[1.0.3] Do not resolve hash-only urls used for routing

[nippur72]

I think the error #651 that was fixed in 0.5 is back in 1.0.

I have an my-element.html that defines:

<a href="#del"></a>

but in the browser it's converted to my-element.html#del.

[nippur72]

I wonder if it's the case of avoiding resolution for urls starting with / too, like we had in 0.5:

polymer/src/lib/url.js

Lines 99 to 101 in c716964

	// do not resolve '/' absolute urls
	if (url && url[0] === '/') {
	return url;