anchor.diff:     stringi_1.1.2.tar.gz \
      magrittr_1.5.tar.gz \
      stringr_1.1.0.tar.gz \
  -   knitr_1.14.tar.gz \
  -   yaml_2.1.13.tar.gz \
  -   Rcpp_0.12.7.tar.gz \
  +   knitr_1.15.1.tar.gz \
  +   yaml_2.1.14.tar.gz \
  +   Rcpp_0.12.8.tar.gz \
      htmltools_0.3.5.tar.gz \
      caTools_1.17.1.tar.gz \
      bitops_1.0-6.tar.gz \
  
positive.code: 
  # update the R packages we will need for knitr
  RUN DEBIAN_FRONTEND=noninteractive wget \
     http://archive.linux.duke.edu/cran/src/contrib/knitr_1.14.tar.gz \
     http://archive.linux.duke.edu/cran/src/contrib/yaml_2.1.13.tar.gz \
     http://archive.linux.duke.edu/cran/src/contrib/Rcpp_0.12.7.tar.gz \
     http://archive.linux.duke.edu/cran/src/contrib/htmltools_0.3.5.tar.gz \
     http://archive.linux.duke.edu/cran/src/contrib/caTools_1.17.1.tar.gz \
     http://archive.linux.duke.edu/cran/src/contrib/bitops_1.0-6.tar.gz \
  
negative.code:    whisker_0.3-2.tar.gz \
     bitops_1.0-6.tar.gz \
     RCurl_1.95-4.8.tar.gz \
     Rcpp_0.12.8.tar.gz \
     plyr_1.8.4.tar.gz \
     R6_2.2.0.tar.gz \
     curl_2.2.tar.gz \
  