Use of readlink in bin/build.sh not portable to BSD/OSX.

[pefribeiro]

Just getting my isabelle-utp installation up to date with the 2017 version of Isabelle.

I really like the build script, but I've found a minor issue which may be worth having in mind in the future:readlink -f is not portable to BSD/OSX-land. Not sure what else to suggest given the difficulty of emulating this. An alternative is to install the GNU version of readlink.

utp-main/bin/build.sh

Line 3 in ce90795

ISABELLE_UTP=${ISABELLE_UTP:-$(readlink -f $(dirname $0))/..}

Instead, I set export ISABELLE_UTP=`pwd` from my clone folder of the repo and then ran the bin/build.sh file just fine.