fix failure when running with NODE_DEBUG=request, and a test for that

lib/debug.js

@@ -1,5 +1,7 @@
+var util = require('util')
+
 module.exports =
 function debug () {
   if (/\brequest\b/.test(process.env.NODE_DEBUG))
     console.error('REQUEST %s', util.format.apply(util, arguments))
-}
+}

tests/test-node-debug.js

@@ -0,0 +1,18 @@
+var assert = require('assert')
+  , request = require('../index')
+  , http = require('http')
+  ;
+
+var s = http.createServer(function(req, res) {
+  res.statusCode = 200
+  res.end('')
+}).listen(6767, function () {
+  // a simple request should not fail with NODE_DEBUG
+  process.env.NODE_DEBUG = 'mumblemumble,request'
+
+  request('http://localhost:6767', function (err, resp, body) {
+    assert.ifError(err, 'the request did not fail')
+    assert.ok(resp, 'the request did not fail')
+    s.close(); // clean up
+  })
+})