Fix canonifyurl vs schemaless links

Fix canonifyurl vs schemaless links

And looks even faster:

Compared to previous attempt:

benchmark              old ns/op     new ns/op     delta
BenchmarkAbsUrl        30902         27206         -11.96%
BenchmarkXmlAbsUrl     15389         14216         -7.62%

benchmark              old allocs     new allocs     delta
BenchmarkAbsUrl        33             28             -15.15%
BenchmarkXmlAbsUrl     16             14             -12.50%

benchmark              old bytes     new bytes     delta
BenchmarkAbsUrl        4167          3504          -15.91%
BenchmarkXmlAbsUrl     2057          2048          -0.44%

Compared to before I started all of this:

benchmark              old ns/op     new ns/op     delta
BenchmarkAbsUrl        36219         27206         -24.88%
BenchmarkXmlAbsUrl     23903         14216         -40.53%

benchmark              old allocs     new allocs     delta
BenchmarkAbsUrl        60             28             -53.33%
BenchmarkXmlAbsUrl     30             14             -53.33%

benchmark              old bytes     new bytes     delta
BenchmarkAbsUrl        5842          3504          -40.02%
BenchmarkXmlAbsUrl     3754          2048          -45.44%

Fixes #816