add and release cleaner for gthumb (https://wiki.gnome.org/Apps/gthumb)
gThumb is an advanced image viewer and browser for the GNOME Desktop
this cleaner deletes the history of recenlty used files in gThumb
Merge pull request #49 from nodiscc/master

Add and release cleaner for gthumb (https://wiki.gnome.org/Apps/gthumb; thanks to nodiscc)