Fixed #13725 -- take url scheme into account in assertRedirects

Scheme is handled correctly when making comparisons between two URLs. If
there isn't any scheme specified in the location where we are redirected to,
the original request's scheme is used. If present, the scheme in
``expected_url`` is the one used to make the comparations to.
Merge pull request #1850 from unaizalakain/ticket_13725

Fixed #13725 -- take url scheme into account in assertRedirects

Thanks to Loic for review.