Vendor code using godep.

For 3rd parties building binary packages, and for build consistency in
general, it is very helpful to have the same set of dependencies at
any time the product is built.

See [tools/godep](https://github.com/tools/godep) for further details.

vendor/github.com/codegangsta/negroni/response_writer_pusher.go

@@ -0,0 +1,16 @@
+//+build go1.8
+
+package negroni
+
+import (
+	"fmt"
+	"net/http"
+)
+
+func (rw *responseWriter) Push(target string, opts *http.PushOptions) error {
+	pusher, ok := rw.ResponseWriter.(http.Pusher)
+	if ok {
+		return pusher.Push(target, opts)
+	}
+	return fmt.Errorf("the ResponseWriter doesn't support the Pusher interface")
+}