Fix subapp.mountpath regression for app.use(subapp)

fixes #2233
4.6.1
perf: prevent multiple Buffer creation in res.send
Add configurable query parser

closes #2215
Change req.host to return host
Remove res.send(body, status) signature
Remove res.json(obj, status) signature
Remove res.jsonp(obj, status) signature
Remove app.router error message
Change req.query to a getter
Refactor away init middleware
Add app.router reference back