If the new package is the ICD rather than the loader, why is it called
libopencl1-mesa rather than mesa-opencl-icd? Consistency with the
others would suggest the latter.
Due to unsupported hardware, I can't tell you whether it actually works;
you might want to join the current discussion at
http://lists.alioth.debian.org/pipermail/pkg-opencl-devel/ of how we
should choose which ICD(s) to install/default to.