Port added even if not necessary (http:80 / https:443)

[smalot]

When proxy is listening on port 80, url integrates the ":80" just after the hostname. Many framework, like Symfony don't support such url because it's really uncommon:

http://client.local:80/homepage

Instead we should have such url:

http://client.local/homepage

[smalot]

The function "_getDefaultPort()" is responsible of this issue. Setting the "port" property to null seems to be supported is the "ProvisionableRequest" class.