View-only mode doesn't need keyboard or mouse

Grabbing the keyboard and mouse is unnecessary in view_only mode.
In fact its unnecessary to create the objects at all. Fixes #644.

include/rfb.js

@@ -184,6 +184,7 @@ var RFB;
             throw exc;
         }
 
+        if (!this._view_only) {
             this._keyboard = new Keyboard({target: this._focusContainer,
                                            onKeyPress: this._handleKeyPress.bind(this)});
 
@@ -191,6 +192,7 @@ var RFB;
                                      onMouseButton: this._handleMouseButton.bind(this),
                                      onMouseMove: this._handleMouseMove.bind(this),
                                      notify: this._keyboard.sync.bind(this._keyboard)});
+        }
 
         this._sock = new Websock();
         this._sock.on('message', this._handle_message.bind(this));