another benchmark optimisation

Demos/benchmarks/nbody.pxd

@@ -9,7 +9,7 @@ cdef combinations(list l)
 cdef advance(double dt, long n, list bodies=*, list pairs=*)
 
 @cython.locals(x1=double, x2=double, y1=double, y2=double, z1=double, z2=double,
-               m1=double, m2=double, vx=double, vy=double, vz=double)
+               m=double, m1=double, m2=double, vx=double, vy=double, vz=double)
 cdef report_energy(list bodies=*, list pairs=*, double e=*)
 
 @cython.locals(vx=double, vy=double, vz=double, m=double)