[Rd] Add "..." argument to generic of "median"

[Andreas Eckner]

Dear developers,
 
would it be feasible to add an "..." argument to the "median" generic
function (and by extension also to "median.default")?

That would allow the implementation of "median" methods for data structures
that require optional arguments, as is already supported by the "mean"
generic function. 

Best,
Andreas