GUCAMOLE-206: Merge fix for dropped keys while alt pressed.
GUCAMOLE-206: Merge fix for dropped keys while alt pressed.

glyptodon/guacamole-server,apache/guacamole-server,glyptodon/guacamole-server,apache/guacamole-server,mike-jumper/incubator-guacamole-server,apache/guacamole-server,mike-jumper/incubator-guacamole-server,glyptodon/guacamole-server,mike-jumper/incubator-guacamole-server,mike-jumper/incubator-guacamole-server