more images than GIF supported

Use of the Tk::Img library was added to CORE. This allows you to use various image types besides just the GIFs that were supported before -- such as JPG, PNG, TIF, etc. Now the custom node icon and canvas wallpaper dialogs accept various image types.

The Img library is a new dependency for the CORE GUI. You can install it with:

    # for RedHat/Fedora
    yum install tkimg

or

    # for Debian/Ubuntu
    sudo apt-get install libtk-img