net/url: URL should parse the port number and store it separately

[foresmac]

The port number from a URL should not be left tacked on the end of the host when parsing a URL into a url.URL struct. Instead, the port number should be pulled out and added to a url.URL.Port field. Leaving the port in a parsed hostname invariably leaves developers calling strings.Split(url.URL.Host, ":")[0] repeatedly to get the hostname.

[foresmac]

For instance:

http://www.example.com:4000/example/path?page=42

Should parse to:

url.URL{"http", "", nil, "www.example.com", 4000, "/example/path", "page=42", ""}

[minux]

First of all, port is part of the host in RFC 2616.
And more importantly, this is a backward incompatible change, so
even if we want to add a Port field to net/url.URL, we can't.

[foresmac]

Fair enough.