[Rd] Broken link in R-exts.html

[Matt Shotwell]

The HTML link 'Customizing package compilation' in 'Writing R 
Extensions' is broken. See the offending link near here:
http://cran.r-project.org/doc/manuals/R-exts.html#Submitting-a-package-to-CRAN

In R-exts.texi, it looks like a five-argument @xref was intended. Oddly, 
the PDF link works anyway. This fixes the HTML link for me; doesn't 
break the PDF link:

Index: doc/manual/R-exts.texi
===================================================================
--- doc/manual/R-exts.texi      (revision 55161)
+++ doc/manual/R-exts.texi      (working copy)
@@ -2104,7 +2104,7 @@
  Collection.  If @R{} was not configured accordingly, one can achieve
  this @emph{via} personal @file{Makevars} files.
  @ifset UseExternalXrefs
- at xref{Customizing package compilation,
+ at xref{Customizing package compilation, ,
  Customizing package compilation, R-admin,
  R Installation and Administration},
  @end ifset

-- 
Matthew S Shotwell   Assistant Professor           School of Medicine
                      Department of Biostatistics   Vanderbilt University