anchor.diff:  
   FROM centos:6
   MAINTAINER Luke Heidecke <luke@solinea.com>
  +
  +ENV RERUNVER=1.3.4-1.el6
  +ENV DISCOUNTVER=2.1.8a
  +ENV PYGMENTSVER=2.0.2
   
   ENV APPDIR /app
   WORKDIR $APPDIR
  
positive.code:     yum clean all
  
  # install pygments
  RUN pip install pygments
  
  # environment variables
  ENV PATH ${PATH}:$APPDIR/bin
  
negative.code:     yum clean all
  
  # install rerun
  RUN rpm -Uvh http://dl.bintray.com/rerun/rerun-rpm/rerun-$RERUNVER.noarch.rpm
  
  # compile and install discount markdown library
  ENV DISCOUNTURL http://www.pell.portland.or.us/~orc/Code/discount/discount-$DISCOUNTVER.tar.bz2
  RUN wget $DISCOUNTURL && \
      tar jxf discount-$DISCOUNTVER.tar.bz2 && \
  