fix($location): make legacy browsers behave like modern ones in html5Mode

Previously, LocationHashbangInHtml5Url, which is used when html5Mode is enabled
in browsers which do not support the history API (IE8/9), would behave very
inconsistently WRT relative URLs always being resolved relative to the app root
url.

This fix enables these legacy browsers to behave like history enabled browsers,
by processing href attributes in order to resolve urls correctly.

Closes #6162
Closes #6421
Closes #6899
Closes #6832
Closes #6834