Replace another 'MultiIndex' by '::MultiIndex'

To prevent confusion with a class of the same name in
dune-localfunctions.

test/cosseratenergytest.cc

@@ -365,7 +365,7 @@ int main(int argc, char** argv)
     // Set up elements of SO(3)
     std::vector<TargetSpace> corners(domainDim+1);
 
-    MultiIndex index(domainDim+1, nTestPoints);
+    ::MultiIndex index(domainDim+1, nTestPoints);
     int numIndices = index.cycle();
 
     for (int i=0; i<numIndices; i++, ++index)