The file turt-transparent.xcf is the highest-resolution version available
of the turtle logo. It is not used in runtime in that high-res version but 
instead converted to 2 smaller resolutions before build. 

If you modify the high-res original, have imagemagick installed and say
"make all" in this directory to produce the smaller-resolution versions
that are then used at compile+install stages. Smaller-resolution versions
reside at folder ../ui/.
