[Rd] mosaicplot() update and clarification

[Achim Zeileis]

Torsten, thanks for pointing this out. 

Jay, just to expand a little on this explanation:

> `mosaicplot' is a function in package `graphics' (and lists you as the
> author) and `mosaic' is a function in package `vcd'. There _was_ a
> function `vcd::mosaicplot' in older versions of the `vcd' package
> masking`graphics::mosaicplot: `update.packages("vcd")' will update the
> package and documentation on your system :-)

The reason for these changes in vcd is the following: When we started
the project we just extended the mosaicplot() function from graphics
(which is based on your code) in a few directions but keeping it
upwardly compatible. Therefore, we decided that it's ok to overload the
graphics function.
Rather soon we wanted something based on grid and something which can be
more easily modified and extended and we've written about three (I
think) new implementations in grid. As the interface needed to be quite
different from the original one, we decided that it wouldn't be
appropriate to overload the graphics function and hence chose a new
function name mosaic(). The corresponding man page still has Emerson
(1998) in the references but does not mention you as the author (as it
is enitrely new code).

Best,
Z