[Rd] Rdconv --type=Ssgm drops singleton keywords (PR#9051)

[bill at insightful.com]

If an Rd file has only one keyword entry then
the Splus sgm file made with Rdconv --type=SSgm
has no keyword entries.

To reproduce:
   Use prompt() to make a skeleton help file
      R> f<-function(x)log(1+x)-log1p(x)
      R> prompt(f)
      Created file named 'f.Rd'.
      Edit the file and move it to the appropriate directory.
      R> q()
   It has 2 \keyword entries in it
      % grep keyword f.Rd
      \keyword{ ~kwd1 }% at least one, from doc/KEYWORDS
      \keyword{ ~kwd2 }% __ONLY ONE__ keyword per line
   If you convert it to the Splus sgm format you get 2
   <s-keyword> entries, in a <s-keywords> section:
      % R CMD Rdconv --type=Ssgm f.Rd | grep 'keyword'
      <s-keywords>
      <s-keyword>~kwd1</s-keyword>
      <s-keyword>~kwd2</s-keyword>
      </s-keywords>
      %
   That is good.

   If you remove one keyword entry from the Rd file so it has one left
   then the sgm file has no <s-keyword> entries (and no <s-keywords>
   section):
      % grep -v '~kwd2' < f.Rd > f1kw.Rd
      % grep keyword f1kw.Rd
      \keyword{ ~kwd1 }% at least one, from doc/KEYWORDS
      % R CMD Rdconv --type=Ssgm f1kw.Rd | grep s-keyword
      %

The fix:
   The problem is that the line
      if ($#keywords > 0) {
   should use >= 0 to tell if the list @keywords is non-empty.

*** share/perl/R/Rdconv.pm	2006-05-23 08:51:16.000000000 -0700
--- /tmp/Rdconv.pm	2006-06-30 11:51:53.000000000 -0700
***************
*** 2965,2971 ****
      Ssgm_print_block_named("references", "References");
      Ssgm_print_seealso();
      Ssgm_print_examples();
!     if ($#keywords > 0) {
  	print $sgmlout "<s-keywords>\n";
  	while ($#keywords >= 0) {
  	    print $sgmlout "<s-keyword>", shift( @keywords ),
--- 2965,2971 ----
      Ssgm_print_block_named("references", "References");
      Ssgm_print_seealso();
      Ssgm_print_examples();
!     if ($#keywords >= 0) {
  	print $sgmlout "<s-keywords>\n";
  	while ($#keywords >= 0) {
  	    print $sgmlout "<s-keyword>", shift( @keywords ),


--please do not edit the information below--

Version:
 platform = i686-pc-linux-gnu
 arch = i686
 os = linux-gnu
 system = i686, linux-gnu
 status = Under development (unstable)
 major = 2
 minor = 4.0
 year = 2006
 month = 06
 day = 29
 svn rev = 38459
 language = R
 version.string = R version 2.4.0 Under development (unstable) (2006-06-29 r38459)

Locale:
LC_CTYPE=en_US.UTF-8;LC_NUMERIC=C;LC_TIME=en_US.UTF-8;LC_COLLATE=en_US.UTF-8;LC_MONETARY=en_US.UTF-8;LC_MESSAGES=en_US.UTF-8;LC_PAPER=en_US.UTF-8;LC_NAME=C;LC_ADDRESS=C;LC_TELEPHONE=C;LC_MEASUREMENT=en_US.UTF-8;LC_IDENTIFICATION=C

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