bash-only syntax used in setenv.sh

There are bashisms in the setenv.sh. On Ubuntu system startup.sh complains with

git@hybe:~$ current/bin/startup.sh
/srv/git/current/bin/setenv.sh: 106: [[: not found

Ubuntu and other Linux flavours are not using bash as system shell (aka /bin/sh). See https://wiki.ubuntu.com/DashAsBinSh#A.5B.5B for differences