Fix bugs reported by Timothy Hunter:

* CholeskyWithoutSqrt with 1x1 matrices
 * .part<Diagonal>()
Updated unit tests to handle these cases

test/cholesky.cpp

@@ -79,7 +79,6 @@ template<typename MatrixType> void cholesky(const MatrixType& m)
   }
   #endif
 
-  if (rows>1)
   {
     CholeskyWithoutSquareRoot<SquareMatrixType> cholnosqrt(symm);
     VERIFY(cholnosqrt.isPositiveDefinite());