Add OpenMP annotations on pairwise distance example.
Add OpenMP annotations on pairwise distance example.

The speedup is not great due to conversion cost.

hainm/pythran,pbrunet/pythran,pbrunet/pythran,pombredanne/pythran,hainm/pythran,artas360/pythran,pombredanne/pythran,artas360/pythran,artas360/pythran,hainm/pythran,pombredanne/pythran,pbrunet/pythran,serge-sans-paille/pythran,serge-sans-paille/pythran