anchor.diff:  ENV \
     HOME=/home/backups \
     BACKUP_CONFIG_DIR=/etc/backups \
  -  BACKUP_DATA_DIR=/var/lib/backups
  +  BACKUP_DATA_DIR=/var/lib/backups \
  +  PG_VERSION=9.6.1
   
   # Install base packages.
   RUN \
  
positive.code:     libxml2-dev \
      libxslt-dev \
      mysql-client \
      postgresql \
      redis \
      rsync \
      ruby \
  
negative.code:     tar \
      zlib-dev && \
    rm -rf /var/cache/apk/*
  
  # Install postgresql
  RUN wget ftp://ftp.postgresql.org/pub/source/v$PG_VERSION/postgresql-$PG_VERSION.tar.bz2 -O /tmp/postgresql-$PG_VERSION.tar.bz2 && \
      tar xvfj /tmp/postgresql-$PG_VERSION.tar.bz2 -C /tmp && \
      cd /tmp/postgresql-$PG_VERSION && \
      ./configure --enable-integer-datetimes --enable-thread-safety --prefix=/usr/local --with-libedit-preferred --with-openssl && \
      make world && \
      make install world && \
      make -C contrib install && \
      cd /tmp/postgresql-$PG_VERSION/contrib && \
      make && make install && \
      rm -r /tmp/postgresql-$PG_VERSION*
  
  # Install ruby gems.
  RUN \
  