Update copyright headers to 2009.

common/panel-dbus.h

common/panel-private.h

libxfce4panel/libxfce4panel.h

libxfce4panel/xfce-arrow-button.c

libxfce4panel/xfce-arrow-button.h

libxfce4panel/xfce-hvbox.c

libxfce4panel/xfce-hvbox.h

libxfce4panel/xfce-panel-convenience.c

libxfce4panel/xfce-panel-convenience.h

libxfce4panel/xfce-panel-enums.h

libxfce4panel/xfce-panel-macros.h

libxfce4panel/xfce-panel-plugin-provider.c

libxfce4panel/xfce-panel-plugin-provider.h

libxfce4panel/xfce-panel-plugin.c

libxfce4panel/xfce-panel-plugin.h

libxfce4panel/xfce-scaled-image.c

libxfce4panel/xfce-scaled-image.h

panel/main.c

panel/panel-application.c

panel/panel-application.h