Kitware Robot authored Jul 05, 2018 and Brad King committed Jul 05, 2018

Populate a script with `map_<md5>=<sha512>` variable settings and
then run the following to convert the content link files:

    git ls-files -- '*.md5' | while read f; do
      md5="$(cat "$f")"
      sha512="$(eval echo \${map_$md5})"
      rm "$f"
      echo $sha512 > ${f%.md5}.sha512
    done

This follows up commit 0d89f23f (ExternalData: Convert content links
from MD5 to SHA512, 2018-05-18) to convert content links added in topic
branches that started before the main conversion.