title: pandoc and rmarkdown: Can't fetch an image one level above a rmarkdown document
body: <p>I am just starting to use rmarkdown, pandoc and knitr. I am having a great deal of difficult trying to get pandoc to fetch an image that is one level above an  rmarkdown document. For example, consider our project directory is ~/test, the following rmarkdown is located at ~/test/scripts:</p>
  
  <pre><code>---
  title: "test"
  ---
  
  ```{r global_options, include=FALSE}
  library('knitr')
  opts_knit$set(root.dir = '~/test')
  ```
  
  ![test](figures/test.svg)
  </code></pre>
  
  <p>I then run the command <code>Rscript -e "rmarkdown::render('scripts/test.Rmd')"</code> from the ~/test directory. And it gives me the error:</p>
  
  <pre><code>pandoc: Could not fetch figures/test.svg
  figures/test.svg: openBinaryFile: does not exist (No such file or directory)
  </code></pre>
  
  <p>I would have thought by setting the root.dir to be the project directory, that pandoc will fetch files relative to that? But it seems that the "working directory" is always set to relative to the where the rmarkdown document is? Any help would be appreciated. Thanks,</p>
  
  <pre><code>&gt;sessionInfo()
  R version 3.1.0 (2014-04-10)
  Platform: x86_64-unknown-linux-gnu (64-bit)
  
  locale:
   [1] LC_CTYPE=en_CA.UTF-8       LC_NUMERIC=C               LC_TIME=en_CA.UTF-8        LC_COLLATE=en_CA.UTF-8     LC_MONETARY=en_CA.UTF-8    LC_MESSAGES=en_CA.UTF-8
   [7] LC_PAPER=en_CA.UTF-8       LC_NAME=C                  LC_ADDRESS=C               LC_TELEPHONE=C             LC_MEASUREMENT=en_CA.UTF-8 LC_IDENTIFICATION=C
  
  attached base packages:
  [1] stats     graphics  grDevices utils     datasets  methods   base
  
  other attached packages:
  [1] vimcom_1.0-0   setwidth_1.0-3 colorout_1.0-2
  
  loaded via a namespace (and not attached):
  [1] tools_3.1.0`
  </code></pre>