Fix double free of parser on error in http.Agent.

Thanks to Stéphan Kochen for the fix and Maurice Fonk for reproducing the
bug.

Closes GH-784.
Closes GH-803.

lib/http.js

@@ -1199,7 +1199,6 @@ Agent.prototype._establishNewConnection = function() {
     parser.finish();
     socket.destroy();
     self._removeSocket(socket);
-    parsers.free(parser);
     self._cycle();
   });
 

test/simple/test-regress-GH-784.js

@@ -0,0 +1,136 @@
+// Regression test for GH-784
+// https://github.com/joyent/node/issues/784
+//
+// The test works by making a total of 8 requests to the server.  The first
+// two are made with the server off - they should come back as ECONNREFUSED.
+// The next two are made with server on - they should come back successful.
+// The next two are made with the server off - and so on.  Without the fix
+// we were experiencing parse errors and instead of ECONNREFUSED.
+var common = require('../common');
+var http = require('http');
+var assert = require('assert');
+
+
+var server = http.createServer(function(req, res) {
+  var body = '';
+
+  req.setEncoding('utf8');
+  req.on('data', function(chunk) {
+    body += chunk;
+  });
+
+  req.on('end', function() {
+    assert.equal('PING', body);
+    res.writeHead(200);
+    res.end('PONG');
+  });
+});
+
+
+server.on('listening', pingping);
+
+
+function serverOn() {
+  console.error("Server ON");
+  server.listen(common.PORT);
+}
+
+
+function serverOff() {
+  console.error("Server OFF");
+  server.close();
+  pingping();
+}
+
+var responses = []
+
+
+function afterPing(result) {
+  responses.push(result);
+  console.error('afterPing. responses.length = ' + responses.length);
+  switch (responses.length) {
+    case 2:
+      assert.ok(/ECONNREFUSED/.test(responses[0]));
+      assert.ok(/ECONNREFUSED/.test(responses[1]));
+      serverOn();
+      break;
+
+    case 4:
+      assert.ok(/success/.test(responses[2]));
+      assert.ok(/success/.test(responses[3]));
+      serverOff();
+      break;
+
+    case 6:
+      assert.ok(/ECONNREFUSED/.test(responses[4]));
+      assert.ok(/ECONNREFUSED/.test(responses[5]));
+      serverOn();
+      break;
+
+    case 8:
+      assert.ok(/success/.test(responses[6]));
+      assert.ok(/success/.test(responses[7]));
+      server.close();
+      // we should go to process.on('exit') from here.
+      break;
+  }
+}
+
+
+function ping() {
+  console.error("making req");
+
+  var opt = {
+    port: common.PORT,
+    path: '/ping',
+    method: 'POST'
+  };
+
+  var req = http.request(opt, function(res) {
+    var body = '';
+
+    res.setEncoding('utf8');
+    res.on('data', function(chunk) {
+      body += chunk;
+    });
+
+    res.on('end', function() {
+      assert.equal('PONG', body);
+      assert.ok(!hadError);
+      gotEnd = true;
+      afterPing("success");
+    });
+  });
+
+  req.end('PING');
+
+  var gotEnd = false;
+  var hadError = false;
+
+  req.on('error', function(error) {
+    console.log("Error making ping req: " + error);
+    hadError = true;
+    assert.ok(!gotEnd);
+    afterPing(error.message);
+  });
+}
+
+
+
+function pingping() {
+  ping();
+  ping();
+}
+
+
+pingping();
+
+
+
+
+process.on('exit', function() {
+  console.error("process.on('exit')");
+  console.error(responses);
+
+  assert.equal(8, responses.length);
+});