title: R package warning: Files in the 'vignettes' directory newer than all files in 'inst/doc'
body: <p>In an R package I have two legacy Sweave vignettes as <code>.Rnw</code> files.  When I check the package locally (in R Studio: Build -> Check), there are no errors, or warnings, and the same thing goes when my package is checked on R-Forge using R version 3.3.1 Patched (2016-10-17 r71531).</p>
  
  <p>However, when I submit the package to Win-builder (via <code>devtools::build_win()</code>) for checking under R devel (unstable) (2016-10-16 r71524)), I get the following warnings that I am unable to resolve:</p>
  
  <pre><code>Files in the 'vignettes' directory newer than all files in 'inst/doc':
    'fig/plot-Ortho-fm1.pdf', 'fig/plot-Ortho-fm3.pdf',
      'fig/plot-grades-can-class.pdf', 'fig/plot-grades-can-gpa.pdf',
      'fig/plot-grades-can-sex.pdf', 'fig/plot-grades-pairs.pdf',
      'fig/plot-hern-can-age.pdf', 'fig/plot-hern-can-build.pdf',
      'fig/plot-hern-can-cardiac.pdf', 'fig/plot-hern-can-pstat.pdf',
      'fig/plot-hern-pairs.pdf', 'fig/plot-jury-can1.pdf',
      ...
  </code></pre>
  
  <p>My package directory structure includes the vignettes in <code>vignettes/</code> and the the result of <code>devtools::build_vignettes()</code> in <code>inst/doc/</code>, as follows:</p>
  
  <pre><code>...
  man/
  inst/
     doc/HE-examples.{pdf,R,Rnw}
     doc/repeated.{pdf,R,Rnw}
  R/
  vignettes/HE-examples.Rnw
           /repeated.Rnw
           /fig/   # all generated fig files
  </code></pre>
  
  <p>The reason that I include the generated <code>.pdf</code> files in <code>inst/doc/</code> is that otherwise I get a warning that the <code>.pdf</code> files need to be compressed with <code>qpdf</code>, and the only way I can actually do this is to open them in Acrobat Pro and re-save as compressed PDF.   </p>
  
  <p>I've tried adding <code>inst/doc</code> to <code>.Rbuildignore</code>, but that generates an error.  I also tried adding <code>inst/doc/*.pdf</code> to <code>.Rbuildignore</code> but that has no effect.</p>
  
  <p>The warning is preventing me from submitting an update to CRAN.  I don't understand why newer files in <code>vignettes/</code> should be a problem, but how can I fix the warning?  </p>