ctx.redirect(): only set status code if not already a valid redirect status code

specifically 3xx codes except for 304. closes #66

lib/context.js

@@ -788,7 +788,7 @@ Context.prototype = {
   redirect: function(url, alt){
     if ('back' == url) url = this.get('Referrer') || alt || '/';
     this.set('Location', url);
-    this.status = 302;
+    if (!~[300, 301, 302, 303, 305, 307].indexOf(this.status)) this.status = 302;
 
     // html
     if (this.accepts('html')) {

test/context.js

@@ -849,6 +849,30 @@ describe('ctx.redirect(url)', function(){
       ctx.body.should.equal('Redirecting to ' + url + '.');
     })
   })
+
+  describe('when status is 301', function(){
+    it('should not change the status code', function(){
+      var ctx = context();
+      var url = 'http://google.com';
+      ctx.status = 301;
+      ctx.header.accept = 'text/plain';
+      ctx.redirect('http://google.com');
+      ctx.status.should.equal(301);
+      ctx.body.should.equal('Redirecting to ' + url + '.');
+    })
+  })
+
+  describe('when status is 304', function(){
+    it('should change the status code', function(){
+      var ctx = context();
+      var url = 'http://google.com';
+      ctx.status = 304;
+      ctx.header.accept = 'text/plain';
+      ctx.redirect('http://google.com');
+      ctx.status.should.equal(302);
+      ctx.body.should.equal('Redirecting to ' + url + '.');
+    })
+  })
 })
 
 function escape(html) {