Ok, here is a patch for 8bit jpeg support. Turned out I was looking at the 
original 3 channel backtile.jpg, no wonder it got colors in there, so 8bit 
jpegs *are* greyscale after all - confused me a great deal. Sorry you have to 
deal with a second patch. But this one now supports 8 bit jpegs. 
It works by applying the grey shade to all three color channels, so it should 
result in the same grey.