resolve FIXME from 2003 via new \manual syntax

git-svn-id: https://svn.r-project.org/R/trunk@88885 00db46b3-68df-0310-9c12-caf00c1e9a41

Author: smeyer

src/library/base/man/Extract.Rd

@@ -326,13 +326,10 @@ x$name <- value
   behaviour when applied to data.frame and factors.
 
   \code{\link{Syntax}} for operator precedence, and the
-  \sQuote{R Language Definition} manual about indexing details.
-
+  Section \manual{R-lang}{Indexing}.
 
   \code{\link{NULL}} for details of indexing null objects.
 }
-%% Fixme: Link (to html in 'help.start()', pdf from 'ref manual',
-%% 'info' from ESS), see \url{https://CRAN.R-project.org/manuals.html}.
 
 \examples{
 x <- 1:12