title: Using knitr markdown in RStudio calling two different versions of R (2.15.3 and 3.0.2)
body: <p>I would like to be able to create a Knitr Markdown document
  calling different versions of R (2.15.3 and 3.0.2) from within R studio.Is this possible?
  The reason for this is that some packages that have been discontinued may only 
  work in an older version of R</p>
  
  <p>For example:</p>
  
  <pre><code>Title
  ========================================================
  
  xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
  I would like to run a package from
  R version 2.15.3 (2013-03-01) -- "Security Blanket"
  here:
  xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
  xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
  
  ```{r}
  summary(cars)
  ```
  
  embed plots:
  
  ```{r fig.width=7, fig.height=6}
  plot(cars)
  ```
  xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
  I would like to run a package from
  R version 3.0.2 (2013-09-25) -- "Frisbee Sailing"
  
  here:
  xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
  xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
  
  ``{r}
  summary(cars)
  ```
  
   embed plots:
  
   ```{r fig.width=7, fig.height=6}
   plot(cars)
  </code></pre>
  
  <hr>
  
  <p>I added my output here as too large for the comment box
  Rscript,exe is in:
  C:\Program Files\R\R-2.15.3\bin</p>
  
  <p>```{r,engine='Rscript', engine.path='C/Program Files/R/R-2.15.3/bin/Rscript'}
  version</p>
  
  <p>```</p>
  
  <p>on running KNIT HTML I get the following error</p>
  
  <p>Error in system(cmd, intern = TRUE) : 
    '"C/Program Files/R/R-2.15.3/bin/Rscript"' not found</p>