Query strings are now being passed to backends

```
$ go test
warning: building out-of-date packages:
	github.com/kr/spdy/spdyframing
installing these packages with 'go test -i' will speed future tests.

PASS
ok  	_/Users/relsmore/Development/spdy	0.085s
```

Haven't added in tests for query strings yet, just edited the current tests to support the header.