[bugfix] Projection onto the normal space of R^n was wrong

That projection is the zero map, not the identity.

[[Imported from SVN: r9843]]

dune/gfe/rigidbodymotion.hh

@@ -271,7 +271,7 @@ public:
 
         // translation part
         for (int i=0; i<N; i++)
-          result[i] = v[i];
+          result[i] = 0;
 
         // rotation part
         T sp = 0;