[Rd] Wish: add link to Date in date help page

[Gregor Gorjanc]

Hello!

Could someone add Date to see also links in date help page i.e. the
following code in ./src/library/base/man/date.Rd

\seealso{
  \code{\link{Sys.time}} and \code{\link{Date}}
}

I always fire ?date instead of ?Date and I guess a lot of useRs also get
lost in search for the right help pages about date-time classes.

Btw. Perhaps article from RNews about datetime classes by Gabor and
Thomas could also be added to "all?" date-time help pages. That article
really rocks and I guess it would help a lot to provide link from help
pages. This is not the first wish about this issue. I can provide
patches if this wish is accepted!

Thanks!

Gregor