[Rd] Revised help pages for methods package

[John Chambers]

A number of the help pages have been revised, so far only on the r-devel 
version, although the great majority of the revisions apply to 2.7.0 as 
well.

Much of the existing documentation is out of date, some of it badly.  
Also, a goal of the revision is that readers could start with 
package?methods and navigate down through some general pages to 
details.  (Not by any means as an introduction to the topic, but for 
clarifications and for details.)

I hope eventually to revise most of the pages, but only a dozen or so 
have been done at this point (including, however, many of the key 
topics).   Another reason for delay was that the new pages reference the 
"Software for Data Analysis" book, which was supposed to be out by now, 
but is not "quite" (questions on that topic have to go to the publisher).

However, it seems useful to distribute these revisions now, as the 
topics come up, for example, in this mailing list fairly often.

John