Fix many long to int conversion warnings:

- fix usage of Index (API) versus StorageIndex (when multiple indexes are stored)
 - use StorageIndex(val) when the input has already been check
 - use internal::convert_index<StorageIndex>(val) when val is potentially unsafe (directly comes from user input)

Eigen/src/SparseLU/SparseLU_pruneL.h

@@ -124,7 +124,7 @@ void SparseLUImpl<Scalar,StorageIndex>::pruneL(const Index jcol, const IndexVect
           }
         } // end while 
         
-        xprune(irep) = kmin;  //Pruning 
+        xprune(irep) = StorageIndex(kmin);  //Pruning 
       } // end if do_prune 
     } // end pruning 
   } // End for each U-segment