pocl_buffer_boundcheck_3d off by 1
pocl_buffer_boundcheck_3d off by 1

I think negating region[0] by - 1 was always yielding a byte size 1 byte 
smaller than intended.

franz/pocl,franz/pocl,pocl/pocl,franz/pocl,pocl/pocl,Oblomov/pocl,Oblomov/pocl,pocl/pocl,pocl/pocl,Oblomov/pocl,Oblomov/pocl,Oblomov/pocl,pocl/pocl,franz/pocl,franz/pocl