fix($location): parse xlink:href for SVGAElements

Before this fix, the xlink:href property of an SVG <a> element could not be parsed
on click, as the property is an SVGAnimatedString rather than a DOMString.

This patch parses the xlink:href's animVal into a DOMString in order to prevent
an `Object #<SVGAnimatedString> has no method 'indexOf'` exception from being thrown,
and also to update the location if necessary as expected.

Closes #5472
Closes #5198
Closes #5199
Closes #4098
Closes #1420
Merge branch 'master' of https://github.com/angular/angular.js