By making this change, we ensure the materials look the same on DarkPlaces and
other engines, even in the case it's wrong on DarkPlaces because Xonotic mappers
now expect the wrong behavior.
Darkplaces only supports one alphaFunc operation, it only reads the alphaFunc
keyword and does not read the function name:
By storing this texture in lossless format and making sure the frame is pure
black and the ladder is a bit less black than pure black, only the frame would
be transparent.
Unfortunately, after years of GE128 usagen displaying the texture with GT0
operation would be a regression.
Note: I also renamed some `alphafunc` to `alphaFunc` even if it was already GE128.