Hello,

Here is a patch to allow the margin value for float option in figure 
environment.

The marginfigure environment is proposed by the LateX sidenotes package 
and is commonly used in book editions. I needed it to edit with 
EmacsOrgmode a book with the Tufte-book class. I could use this new 
export properly and I now want to propose it to the OrgMode users.

Please tell me if the submission procedure is correct,

Louis Gostiaux.