Hello,

Not being the maintainer of calendar, I would like to get your
approval/brickbats/comments before commiting this : the objective is to
make landscape by landscape class option + \usepackage{geometry}, rather
than \special{landscape} in the preamble.

The advantage of this way is that this it works directly if you compile
with pdflatex, rather than latex+dvips+ps2pdf.  To achieve this I had to
change some of the function prototypes, the landscape argument is
removed, and landscape option is passed just as another class option.

BR,
  Vincent.

PS : This would go in the master branch.