Merge QuasiDiagonals?

[jagot]

I need to compute the matrix representation of

R'*D'*A*B*C...*D*R

and similar operators, where A, B, C ... are QuasiDiagonal operators. Adding overloads gets tedious quickly, so I wonder, if one might squash adjacent QuasiDiagonals into one QuasiDiagonal, before materialize?