Emit errors instead of throwing on parse errors

If an error is thrown while creating a Request object, such as when an
unknown resource record type is requested, there's no way for the client
to handle it. The error is thrown before the request is emitted and the
handler is called. This change leaves the underlying error throwing as
it is but catches the error in the server and emits them instead.

server.js

@@ -141,12 +141,16 @@ Server.prototype.on_tcp_connection = function(connection) {
     }
 
     if(length !== null && bytes_received == 2 + length) {
-      // All of the data (plus the 2-byte length prefix) is received.
-      var data = Buffer.concat(bufs)
-        , req = new Request(data, connection)
-        , res = new Response(data, connection)
-
-      self.emit('request', req, res)
+      try {
+        // All of the data (plus the 2-byte length prefix) is received.
+        var data = Buffer.concat(bufs)
+          , req = new Request(data, connection)
+          , res = new Response(data, connection)
+
+        self.emit('request', req, res)
+      } catch (err) {
+        self.emit('error', err);
+      }
     }
   })
 }
@@ -164,10 +168,14 @@ Server.prototype.on_udp = function(data, rinfo) {
                    , 'end'          : function() {}
                    }
 
-  var req = new Request(data, connection)
-    , res = new Response(data, connection)
+  try {
+    var req = new Request(data, connection)
+      , res = new Response(data, connection)
 
-  self.emit('request', req, res)
+    self.emit('request', req, res)
+  } catch (err) {
+    self.emit('error', err);
+  }
 }