Change how aux arrays are passed through to rpn3

[mandli]

Noticed that now some compilers will not allow the call to rpn3 to include explicit mention to aux2. The original line is:

call rpn3(ixyz,maxm,num_eqn,num_waves,num_aux,num_ghost,mx,q1d,q1d, &
          aux2(1,1-num_ghost,2),aux2(1,1-num_ghost,2), &
          wave,s,amdq,apdq)

Instead use : to pass array in case maux=0:

call rpn3(..., aux2(:,1-num_ghost,2), aux2(:,1-num_ghost,2), ...)

This was the only line it complained about, but there may be other places this should be changed. This is also fixed in clawpack/pyclaw#748.