[Rd] fields appearing in cran descriptions pages

[Gabor Grothendieck]

What determines which fields appear in CRAN descriptions pages.
For example, for doBy there is no Date: but there is a vignette listed:

   http://cran.r-project.org/src/contrib/Descriptions/doBy.html

whereas for gsubfn there is a Date: but there is no vignette listed
(even though it has one).

  http://cran.r-project.org/src/contrib/Descriptions/gsubfn.html