Support URLs that have a path component

[micahr]

Combine both PRs #633 and #628

Pull the logic from #633 and clean it up a bit
Pull the tests from #628

Thanks to both @nakosung and @calebbrown for their contributions.

The goal of this PR is to use the path from both the Client options and the requested url.

For example, when a user creates a client for a non-root url, any subsequent requests should use that as part of the request path.

var client = restify.createClient({
    url: 'http://127.0.0.1/str'
});

client.get('/foo', function (err, req, res, data){});

The resulting request should go to http://127.0.0.1/str/foo.

[DonutEspresso]

Based on #692, I think it's safe to say that we probably don't want to strip trailing slashes. Make the users be explicit?

[DonutEspresso]

Also, could probably use url.resolve() in favor of [].join('/');

[micahr]

This wouldn't affect #692 as this is a http client making requests to any other http server / endpoint, not the server managing routes.

url.resolve() won't work if the request url has a / at the beginning, it will replace whatever path is already at the beginning of the path.

url.resolve('/foo/bar', '/baz') === '/baz';

[DonutEspresso]

That's a bummer, maybe we should look into something like URIjs, there's a lot of URL mugging that should be centralized (plugins too).

Re: above sorry, I should have been clearer, I just think that we should be consistent, presumably if users need strict URLs on the server, them they need a client that can hit those strict URLs. If we strip trailing slashes automatically them it's impossible to do so. Maybe we can do a strict:true option?

[micahr]

I agree, we should definitely standardize the management of urls via the server and client libraries.

[yunong]

This is definitely a feature we want. But I'm going to lean on not merging this specific PR. We should figure out the URL interface and standardize on that per what @micahr suggested. Will close and file #846 to that effect.