this.respond=false for bypassing koa's response handling

closes #198

docs/api/context.md

@@ -102,6 +102,12 @@ throw err;
   error messages since you do not want to leak failure
   details.
 
+### ctx.respond
+
+  To bypass Koa's built-in response handling, you may explicitly set `this.respond = false;`. Use this if you want to write to the raw `res` object instead of letting Koa handle the response for you.
+
+  Note that using this is __not__ supported by Koa. This may break intended functionality of Koa middleware and Koa itself. Using this properly is considered a hack and is only a convenience to those wishing to use traditional `fn(req, res)` functions and middleware within Koa.
+
 ## Request aliases
 
   The following accessors and alias [Request](request.md) equivalents:

lib/application.js

@@ -184,6 +184,8 @@ function *respond(next){
 
   yield *next;
 
+  if (false === this.respond) return;
+
   var res = this.res;
   if (res.headersSent || !res.socket.writable) return;
 

test/application.js

@@ -94,6 +94,31 @@ describe('app.use(fn)', function(){
 })
 
 describe('app.respond', function(){
+  describe('when this.respond === false', function(){
+    it('should bypass app.respond', function(done){
+      var app = koa();
+
+      app.use(function *(){
+        this.body = 'Hello';
+        this.respond = false;
+
+        var res = this.res;
+        setImmediate(function () {
+          res.setHeader('Content-Type', 'text/plain');
+          res.end('lol');
+        })
+      })
+
+      var server = app.listen();
+
+      request(server)
+      .get('/')
+      .expect(200)
+      .expect('lol')
+      .end(done);
+    })
+  })
+
   describe('when HEAD is used', function(){
     it('should not respond with the body', function(done){
       var app = koa();