Fix missing control points in async version.

The allocation pool was reallocating the same frame as soon as it had
left the current scope, before it had been copied. We just reallocate
the same chunks. I don't think this has any real performance impact but
this can be verified.

cuburn/code/filtering.py

@@ -241,7 +241,6 @@ void density_est(float4 *pixbuf, float4 *outbuf,
                         de_add(si,  jj, -ii, scaled);
 
                         iif += 1;
-                        // TODO: validate that the above avoids bank conflicts
                     }
                 }
             }