[fix] append http if no scheme is provided in xpath's extact_url
[fix] append http if no scheme is provided in xpath's extact_url

This solves a bug with Yahoo where some results don't specify
a protocol.

asciimoo/searx,asciimoo/searx,asciimoo/searx,dalf/searx,jcherqui/searx,asciimoo/searx,jcherqui/searx,jcherqui/searx,jcherqui/searx,dalf/searx,dalf/searx,dalf/searx