`setup-env.sh` not resilient to being run from various paths/shells.

[nhanford]

I created the following alias:

alias mybenchpark="source /p/vast1/${USER}/github/benchpark/setup-env.sh; source /p/vast1/${USER}/benchout/venv/bin/activate"

However, this failed because setup-env.sh is a one-liner that just:

export PATH=${PWD}/bin:$PATH

which assumes a bash-like shell and that the user is currently in the benchpark clone directory whenever they source the environment. Please harden this for users calling it from anywhere and with various shells.